Blog Post

7 Tips to Get More from Mini-Split Heat Pumps in Colder Climates

Air-to-air heat pumps are getting more popular as a primary heat source in colder climates. Here’s how to get the most from your system.

[Editor's Note: This guest post comes to us courtesy of Peter Talmage, P.E., an energy and design consultant and an instructor in the Renewable Energy & Energy Efficiency program at Greenfield Community College. Originally published April 4, 2013.]

I have heated my various homes with wood since 1975. It was always a love/hate relationship. The wood fuel was “free” off my land, but burning it was a very dirty business in many ways.

Fujitsu 3/4-ton model 9RLS mini split heat pump

This is in its third season as the primary heater for our 1,500 ft2 home in Northfield, Massachusetts. The interior unit is 18" off the floor, and certain creatures like that very much.

Photo: Peter Talmage

Mini-splits in cold climates? Yes we can!

Three years ago, I installed a ¾-ton Fujitsu model air-source mini-split heat pump to heat my historic 1790 cape home here in Northfield, Massachusetts. It has been a great success.

During the winter of 2010–2011, the heater for my 1,500 ft2 home consumed 1,757 kWh from October 2010 to June 2011. For the warmer winter of 2011–2012, the usage was only 1,247 kWh from September 2011 to April 2012.

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So far this winter, from October 2012, to March 23, 2013, the usage has been 1,501 kWh. I have a 5.4 kW PV array that supplies about 200% of my electrical consumption, including that of the heat pump, so the heating system is very “green.” I have since installed mini-splits in two other houses.

Below are my suggestions for successful house-heating with a mini-split—even in a cold, Northern New England climate like mine.

1. Reduce load first

Improve the thermal envelope of the structure to minimize the size you’ll need and to reduce overall energy use.

2. Size it right for typical low temperatures

Heat-pump output drops as the outdoor temperature drops. I recommend sizing the heat pump to meet heating load at, say, 10°F. During periods of lower temperatures, use simple electric resistance heating or another source to make up the difference.

shed roof installed over compressor for mini split heat pump

The compressor in the Massachusetts house is located on the east side of the house and has a shed roof installed over it. The big pile of snow on the left had just slid off the roof cover.

Photo: Peter Talmage

Also, remember that a heat pump doesn’t have the capacity to quickly bring a cold house up to temperature. I set the temperature to 60°F whenever the house is unoccupied temporarily or at night and down to 50°F for extended periods of no occupancy. (At the 50° setting, the interior units typically keep air circulating constantly to prevent overly cold spots from developing.)

3. Prepare for a little noise

The interior unit makes noise—not a lot, but a varying level of whoosh. Make sure you can live with it before you install one. Find an installation and listen. If you like a dead-silent house, a mini-split isn’t for you.

4. Let it snow—but not on your outdoor unit!

The outdoor compressor unit needs to be mounted at least two feet above the ground here in snow country. It also needs to be well protected by a roof or cover that does not restrict airflow but doeskeep snow off and away from the unit.

In normal operation, the evaporator will freeze moisture from the air, which takes some extra energy. This ice is melted off during the defrost cycle. The melt-water drains out under the unit and sometimes forms a small glacier. The energy balance of this evaporator freeze/thaw cycle isn’t all that bad because the ice releases heat as it changes phase.

What can drastically reduce the performance of a heat pump, though, is when the evaporator gets plugged with snow. There is no gain of latent heat here, only energy consumption to melt the snow out. If the evaporator is located so snow can easily be sucked into it, the compressor will spend a great deal of its time melting snow and not heating the house.

mini split on sun porch

The compressor for this Kennebunkport, Maine, home is set up high on a stand on the south side of the house. It draws air from a three-season porch that has glass panels installed in the winter, pulling air up through the gaps in the floorboards. A protective roof will be installed as well. 

Photo: Peter Talmage

My latest mini-split installation has the evaporator drawing air from an enclosed porch space. Air is pulled into the porch at low velocity through the spaces between the floorboards. Snow drops out of the air before it enters the porch, so it can’t plug up the evaporator. A second benefit is that the porch warms up in sunny weather, improving efficiency.

5. Get the low-down on indoor mounting

For heating, the interior unit should be mounted about 18 inches off the floor and should have a good, clear shot into the living space. Mounting the unit low has many benefits for heating:

  • First, it operates more efficiently because it is pulling in cooler air to warm up.
  • Second, the warmed air is blown out across the floor and mixes with the cold air at floor level.
  • Third, the air isn’t blowing directly on occupants, which can cause discomfort in the winter unless the moving air is very warm.
  • Fourth, it is very easy to access the filters for cleaning.

6. Right-size the pipes too

The interior and exterior units need at least 15 feet of piping to ensure no noise transfer from the compressor to the inside unit. Greater lengths of tubing are allowed, depending on the manufacturer, but will lower efficiency.

7. In warmer climes, get maximum efficiency

In colder climates, heat pumps need to strike a balance between efficiency (measured as heating seasonal performance factor, or HSPF) and lower operating temperatures. The warmer your climate overall, the more weight you should put on the efficiency side of the equation.

In central New England and south, go for units that have higher HSPF rating over lower operating temperatures. Most of the time, the compressor will be seeing temperatures of 20°F or higher. Rarely will it be running at –10°F.  The latest Fujitsu 9RLS2 has an HSPF of 12.5 Btu/Wh.

Published June 1, 2018

(2018, June 1). 7 Tips to Get More from Mini-Split Heat Pumps in Colder Climates. Retrieved from

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March 7, 2015 - 7:20 pm

Hi Colleen. Tell me if I have this correct: You outdoor unit is sitting on a cement slab with nothing under the metal feet and there is an 8" space between the back of the unit and the house wall. The downstairs indoor unit is wall mounted with it's top 2 feet down from the ceiling. The upstairs unit is wall mounted with only 4 inches between the bottom of the unit and the floor.

Also could you tell me what the orientation is of the side of the house where the outdoor unit is located. (E,W,N or S)

March 13, 2015 - 12:35 pm

Hi Peter, I am on vacation in sunny, warm Fl right now so I don't have access to my heat pump. Whe I get home I will measure exactly the distances for each unit. Also I am in a condo and the only place to put the outdoor unit is facing west. As far as I can remember the outdoor unit might be raised a couple of inches from the cement slab it sits on. I will take photos next week when I get home. Thank you so much for your reply.

March 7, 2015 - 7:06 pm

If you are switching from one type of heating system to another without doing any efficiency improvements to the thermal envelope it is critical that the new system have enough capacity to equal the output of the old system that was required to maintain the house as warm as you are used to. Most heating systems tend to be oversized, but it is apparent from reading various posts that some folks have replaced large oil heating systems with mini-split heat pumps that are not big enough to do the job. Very efficient houses have had good success with heat pumps, but remember that these houses require little heat to stay warm. If an installer doesn’t do some manner of heat load calculation to verify that the selected heat pump is adequate then I would suggest finding another installer who will. Mini-splits are great heaters, but they can’t work miracles.

As for the cost to heat with a mini-split heat pump, it can be less costly than other forms of heat depending on the cost of the energy source. If electricity goes way up and oil goes way down as has happened this winter in New England the old oil boiler may come out ahead. With $2.40 per gallon oil and an 83% efficiency boiler a 1000 Btu of heat costs 2.1 cents. A heat pump using electricity at $ .24 per kWh and operating at a COP of 2.7 can deliver 1000 Btu at a cost of 2.6 cents. The heat pump does have a big advantage over the oil fired boiler in that you can install a PV array on your house and supply the electricity needed. It's very tough to make you own oil!

March 4, 2015 - 10:55 pm

I have gotten some good and clear answers on this site and am hoping someone can explain this mess...

I do expect that it will probably cost me less in the long run with my 3 mini splits over oil. However, with the cold we have been having, our 1500 kwh of Dec/Jan went to 1750 kwh in Jan/Feb. This was, basically, leaving the temp set in the 60 and being uncomfortably cold. The bill was ridiculous, but reflected our power company's newly jacked-up rates. I expect both the kwh and bill to go down for Feb/Mar, as the new power company (we are deregulated and can choose) would save us over $80.00 off a 1750 kwh bill, and the temps have been slightly warmer.

However, what upsets me, academic tho it be, is that today I received a letter from the power company (the former one, who, while no longer our supplier, is the actual biller and maintains the lines, etc.) telling me that if we exceed 2000
kwh in a month they will force us to their "RT" program, which makes the customer pay even more for any energy use between noon and 8 pm. In other words, curtail your use or else. Since I am using it to keep warm (and am not very warm!) there is something very, very wrong with this picture.

How does one purchase a "green" system to save energy and money and end up being threatened by the utility for using too much energy and warned that you will be spending even more if you don't stop?

This has me very upset as I have never received a letter like this in my life. I do not waste energy, and we never used inordinate amounts of electricity, oil or water. Is this whole mini-split thing a huge mistake on my part?

March 1, 2015 - 3:46 pm

I had a Fujitsu Heat Pump installed in my 1000 sq ft condo. I have one wall unit on the 1st floor and 1 on the second. I had a guy I know that works for an HVAC company install it "on the side" He is a trained and licensed HVAC technician but we live in the Northeast where gas furnaces are the norm. So, his expertise is not heat pumps.

My condo was built in the 80's when there was a gas moratorium so it is 100% electric. The average electric bill in the winter was $500 for the previous owner so when I purchased in Oct 14 I immediately had the heat pump with A/C installed. I am pretty happy with it but I'm a bit unhappy with the install. I think my "friend" was a bit "sloppy". Part of the reason being that he really has no experience with the heat pump as it is very rare in my local area for one to be installed. So, my questions are about the indoor and outdoor units.

The outdoor unit is not 18" from the house it is more like 8"-12". It is also not 4" or more from the cement slab it sits on. The 2nd floor unit is about 4" from the floor. The 1st floor unit is about 2' from the ceiling. I would have preferred it closer to the ceiling but he insisted it couldn't be higher because of the A/C. As far as the 2nd floor unit I was not here when he installed and I was not happy when I saw it. For one thing he cut through the floor and ran the hose through brand new carpet so there is a big hole in the carpet. Also, you can feel the cold air coming through the hole. I stuffed a plastic bag in the hole. I'm worried that the 2nd floor unit should not be so close to the floor and could damage the unit eventually voiding the warranty. Also, the outdoor unit is full of ice in the base. It is not high enough to interfere with the fan blades but it is pretty thick. I am afraid to do anything to get rid of the ice as I don't want to damage anything.

As far as heating the house, so far so good. It does get warmer upstairs that it does down but there were issues with cold air leaking in several places. These have been fixed or are being fixed. I did a complete gut of the condo and it is not quite done yet so there are some draft issues on the 1st floor. I will get a better "read" on performance next winter.

Any advice about my units and the installation? I want to make sure everything is as it should be. I don't want to void a warranty on a $4400 heat/ac system. Thank you for your help.

February 15, 2015 - 11:08 am

The energy balance of this evaporator freeze/thaw cycle isn’t all that bad because the ice releases heat as it changes phase.

When a phase change occurs from solid to liquid, it takes heat which is the opposite of what you state here. Ice does not warm materials around it when it melts, it Sucks the heat in for this phase change to occur.

Be careful about pv cell usage. I can see why you would argue that it's fine to use an inefficient means to produce heat when it's really cold out just because you oversized your pv system and it would go to waste anyway. Those pv cells still took energy to be produced and they're also converting light which could be heat on earth. Sure, what you have is not changing much but just imagine everyone running on solar power, oversized and using it in inefficient ways. It would make the outside colder and your heating needs higher and thus even more efficiency loss overall.

Now, heat pumps are more efficient than electrical heating down to some low temperatures of around 0 degrees. But a very good example of wasted efficiency would be using pv cells to run your electric water heater. The cells get 18% efficiency, the inverter gives 90% and the element is 80%. Before you know it, you'redown 13 percent efficiency to get hot water when you could have stastarted with about 50 to 70 percent efficiency using a solar water heater. With those numbers in mind, I would think a solar water heater would be more efficient in heating your home than pv cells and a heat pump would be. The only advantage to the heat pump I see is more convenient storage of energy and able to use it whenever you want.

February 8, 2015 - 2:14 pm

Dave, you have a perfect situation for a mini-split. Your winter temperatures are to die for. ;- ) With temps between 33 and 43 a good mini-split will operate with a COP over 3. You are correct in that the high mount position is for A/C. All the installation manuals refer to the units as air conditioners and therefore recommend the high on the wall position. Mounting low works great for heating, but you will need to put a bump guard around the unit to stop nuisance shot offs. The heat will distribute well if there isn't a lot of furniture or walls in the way. A 12,000 Btu unit will probably meet your heating load in the warmer periods of the winter, but it all depends on how well insulated and how tight your "smallish" house is. Three cords of wood is a bit of BTU especially considering the mildness of your winter. Getting a 1 ton unit that modulates might be a better choice. All units with DC compressors modulate speed and output to match the demand.

February 8, 2015 - 5:14 pm

Hello Peter;
Thanks so much for the reply. The jury is still out on the air handler location, as we have so few options in our house. I am curious about your views on a corner location for the air handler. Given that the area in question (living, dining, kitchen) is more or less a square area of about 500 square feet with a staircase in the centre, will a corner location be OK? I know it is not ideal, but just wondering if it would be workable. Another location we are looking it is partly over a doorway (from our mudroom; not directly outside). I know this will complicate the install of the condensate and refrigerant lines, but is there another reason to avoid installing an air handler near a door? All the install manuals I have looked at seem to recommend avoiding this, but don't explain why?

While I do go through 3 cords, this is all softwood like douglas fir and western hemlock; not nearly the BTUs of the lovely hardwoods you have in New England! Also, we are at 50 degrees latitude here so not much solar insolation in the winter, on the rare sunny winter days. The units I am looking at are DC inverter so they will provide the modulation you refer to. My house is reasonably well insulated but we have a ton of single glazed windows, which we are not going to replace as we have a "character home" with old fashioned windows. Thanks for any thoughts that you can share!

PS Sorry for rubbing it in but, it is currently 49 F this afternoon with a low temperature forecast of 45 F.

February 2, 2015 - 9:45 pm

I live in the PNW (well Vancouver Island, BC to be precise) and heat our smallish house mostly with wood; about 3 cords of softwood per year does it. But our local utility is offering an $800 rebate on mini-split heat pumps and I'm thinking about a Panasonic CS (CU)-XE9PKUA which maxes at about 12,000 BTUs. I will still use the wood stove but I would like an alternative to the baseboard heaters that I also have. And after 25 years, the "romance" of wood heat is wearing thin (and I'm tired of spending weeks cutting, splitting, stacking wood)!

The air handler will be on the main floor of our home which is about 600 square feet, in one large room that encircles a staircase. Average winter temperatures here are mild; average Jan. temperatures is about 33 F low with a high of 43. I will probably rarely use the pump for a/c as summer temperatures here are pretty mild too. But I have some questions about the air handler location. I am doing the install with the help of plumber friend.

If I want to maximize heat distribution and efficiency, is mounting the air handler 18" off the floor a good idea, as shown in the "7 Tips" section in this forum? All of the other websites/manuals etc recommend the high wall mount, presumably for a/c efficiency. If I mount the air handler in a corner, will the warm air still be distributed efficiently? I just don't have a good location in the middle of a wall so I'm considering a corner. I live on a small relatively isolated Island so advice from HVAC contractors is not easy to come by. Thanks for any advice!

February 2, 2015 - 9:18 pm

Hi Chris,

Looking at your numbers I can't see that anything is really wrong. Your house used about $2000 of oil to heat in a year. At $3.50 per gallon that's about 571 gallons. The Btu content of 571 gallons of oil is 78,798,000. Assume your boiler is delivering 85% of that energy to the actual heating of the house, so your house needed 66,978,300 Btu to heat. The equivalent electricity is 19,630 kWh. If we assume the average COP of the heat pumps to be 2.7 then you would need a total of 7,270 kWh over the heating season. This assumes the house is heated in the same manner as before temperature wise and the degree days are about the same. I assume your total per kWh cost for electricity is probably more like $ .17 when you add in the delivery charge, so 7,270 kWh of electricity would cost you around $1,235. This seems better than $2000. Am I missing something here ? You have to remember that very efficient smaller homes like my Northfield house would heat with about 150 gallons of oil. My heat pump used a total of 1700 kWh of electricity last year to heat the house.


February 3, 2015 - 11:59 am

Thanks Peter...I think my main issue is, as the installers told me when they checked things last week, what I was promised...that I would have comparable heat for less money.

Our oil was over $4.50 a gallon for the past two years at least, so we may not have used at much as you've calculated; still, the difference is probably negligible. I have figured that we spent $2000 on the oil and, when we are back to our pre-rate-hike electric price with a new supplier where we spent $370 for our coldest period last year on average we will be spending $270 this year - certainly savings worth noting. However, that's keeping it at 66 (which leaves the rooms without units quite cold - upping it to 72 or 74 helps) and with the wall unit in the basement really not heating the basement well at all, only the back portion of it. I was promised comfort and savings and it seems I have to choose between one or the other, at least in very cold weather like we are having right now - when they have told me the splits just aren't that efficient (note - they told me that now, not when selling them!)

The posts from you and others on this site have cleared things up for me much more than the installers, the sellers or various websites including Fujitsu's. Thanks very much.

February 2, 2015 - 2:55 pm

Hi Christine,

A couple questions to help me think about your system. On average how much oil per yer have you been using to heat the house ? Which specific models did you install ? What is your total cost per kWhr ?


February 2, 2015 - 4:43 pm

Hi Peter - thanks for your prompt reply.

As far as oil per year I have a 250 gallon tank and we probably used 3 tanks a year or so, but I might be wrong on that because I don't have the records and when they are filling it 1/2 or 3/4 tank at a time you never quite know. I can say that it was $2000 a year budgeted over 10 months, although when the price went up it would get shoved to $300 a month for several months to make up the difference, which started to get so unsettling that the heat pumps looked much better. We always kept the heat pretty low (high 50s when not at home, high 60s when home). The electric heat we only used for a few hours each day unless it was bitterly cold. Our highest electric bill last year, pre-split, was $187.

The models installed are Fujitsu ASUI3RLF (if I'm reading it correctly without my glasses!) for the downstairs wall unit. I don't have the numbers for the two ceiling installed units right here. They seem to be the standard Fujitsu ceiling-mounted units. We were paying about 10 cents per kwh until January when it went to 13 (we are deregulated and I just switched to a company for 9, which has not taken effect yet). I don't know what we were paying last year as my husband was paying the bills online and there are no copies, and the company merged with another and "is no more".

A technician was here the other day and checked the refrigerant and the PSI in the compressor and said it was actually above optimum. He said that because we had the fans on high (and not "auto") they were going all the time and running up the kwh count, especially when the units went into defrost mode, so he reset them. This stopped the blast-furnace chocolate-melting periods the wall unit would occasionally lapse into (and also the blowing of cold air for the most part), but the unit kept running constantly with no shut down (or very rarely, unlike the ceiling units)so the technician is supposed to return.

However, I was told by his supervisor that the problem seems to be with what I was promised by Next Step Living, not with the installers. I will say that I was repeatedly told that three units would more than heat this home and I find that they are satisfactory upstairs and that the heat does drift into the two unused bedrooms and the kitchen (although a NSL rep told me two weeks ago that it's a "partial system" and won't do that - the opposite of what I was told, and the opposite of what references [and people on this site] have said, and more or less contrary to my experience.) The basement wall unit is at the very back of the room (which is probably - very roughly guessing here - about 14x24 feet). This was not the optimal place for it but it was decided it was the best available place and that it would heat the room. I find it usually heats the very back of the room and nothing else, even when set at a very high temp.

I read letters to this blog stating that a 1600 foot home is heated by 2 mini splits and that the $330 a month oil bill is now supplanted y a $30-$50 increase in electric. I would think my experience is comparable except I am not using oil for heat at all, and I have watched my bill, which was $80.00 in October, when we didn't use the system, skyrocket to $130 the next month, $250 and now $334 (taking rate hike into consideration, probably would have been in the high 200 range without the hike). On the electric bill we went from using a very low number of kwh in October, the lowest line on the chart, to the highest in December.

The installers told me that 1500 kwh are not that much. But just going from an $80 to a $200+ bill (at the same rate) in two months shows that almost all of the electric bill is tied to this mini split system.

Is there something wrong with the system here or are we doing something wrong?


Chris Gallo

January 30, 2015 - 5:02 pm

I had a Fujitsu mini-split system installed in April. Only 3 units - two ceiling-mounted ones upstairs and one wall unit in the finished half of basement.

The house is a very small ranch (1957). Only two of us so electricity use was always low. Even with electric baseboard heat in the basement our electric bill ran about $150 at the worst. But as oil kept climbing (and we had never had AC) I thought this might be a good idea so after speaking to several references it was done.

We didn't use it for heat until the end of October. The bill was over $200 for the November/December period and a whopping $344 for December/January ($170 last year). Some of that was due to a rate hike but nothing can obscure the fact that we used 1500 kwh for that period. This was keeping the 3 units at 66 and walking around with heavy sweaters and blankets. The company came out and told me everything appears to be working well. I am still waiting for a technician to come, but I cannot figure out why we are using such an astronomical amount of electricity with this system.

At this point, and with oil low, I am very much considering tabling the system for the rest of the winter. I have already contacted my town's Energy Council, the entity that championed this system. The head of that group wanted to know what was up as she intended to install a system in a new house in Maine when she leaves this area (CT) and believe me she was not happy. Not exactly what Green Energy wants. HELP!

April 5, 2015 - 3:08 am

Hi Christine. I don't have 1 of these units yet, but have spent the last couple days researching them extensively. Although your information has been helpful, there are still some areas of question that I have. You gave a model number that came off the wall unit. The same wall units can be used on different efficiency models. Can you pull your contract out and give us the specifics of the model from that along with BTU?

The Fujitsu brand is what I am interested in personally, based on what some of their models offer. Let me try to explain something...Fujitsu is a brand name much like General Motors. You can get a Cobalt from GM just like you can a Cadillac. True, they are both cars, but they are in a different class. Some of the Fujitsu models range from 15-33 SEER, which has to do with the efficiency of each model. Furthermore, some of their models provide energy efficient heat at much lower outside temperatures than other models. Based on what you paid, I would hope you received a higher rated model. If they managed to sell you a lower SEER model, it could cause you to use more energy. If your model isn't one of their better models, your outside temperatures may be too cold for it to heat efficiently. Off the top of my head, I think some of their models will only provide good heat down to 10 degrees F while other models go as low as -15. If your outside temp is close to 0 degrees and your units are only rated to 10, it could cause it to run at it's highest output continuously and still not be able to satisfy your set temperature.

You also said even after setting fan to auto, it was still blowing air during defrost. From what I recall, the inside fans/blowers on all these units are supposed to shut off while it is in the defrost cycle so that it won't blow cold air.

Another long shot is your basement. You mentioned you had electric baseboards and had a Fujitsu installed there. Is it possible that your electric baseboards are still on and if your heat pump function (Heat, Cool, Auto, Dehumidify) is set to Auto, the baseboards are putting out heat and the heat pump thinks it needs to be running on Cool to get to your setpoint? I used to work for a major brick and mortar retailer doing store maintenance at several stores. When I first started, utilities were ridiculous and I found that 1 thermostat was set on cool and the next 1 that was 40 feet away was set on heat. As the air from these 2 adjacent units was blowing back and forth, it was causing both thermostats to sense the units needed to run and they were actually working against each other.

You also mentioned you had the thermostat of 1 of your 3 new units set to 76, yet you said the temps were only getting into the 60's. Did I read that correctly?

My last suggestion would be to get a different company to come out and just check the units. It sounds like there was a conflict between the company who sold it to you and the installing technician since the seller made 1 claim and the tech contradicted it. I don't mean to sound rude, but I have seen my share of salesmen and service techs who are liars or crooks. The service tech already told you your bill had been so high because the fan was running all the time. Not true. The fans on these units only require around 40 watts to run on high. You would have to run it for 25 hours to use 1kwh, which would be less than 20 cents a day. As I mentioned earlier, I have problems with the integrity of some of these service techs. There are many shortcuts they can take installing units and the general public would never know they did it. Sounds like this guy was just trying to give you an answer you could believe and get out of there. Many of the service techs out there aren't very experienced in installing these units, but they won't tell you that. Just because they come in driving a van with a company name on it and wear a uniform, doesn't mean they know everything there is about these units. They just don't want you to know that. They just want to install them as quick as they can and get out of there.

Did you possibly get bids from other companies before agreeing on the the purchase price? You never mentioned the btu output or tonnage of each unit, but that does seem like alot of money for 3 units if your house is small, as you mentioned.

I wish you the best of luck with your new units. As you already know, your electrical usage is going to be higher than before since these are all electric units. The advantage is that you are no longer having to buy oil. As long as your long-term electrical usage is less than you were spending annually for oil, I would say you will come out ahead.

February 2, 2015 - 4:57 pm

Your results don't seem like they would be off, but would have to know the prior numbers.
You need to do a relative comparison, additional kwh over last year, compared to th heating oil used, converted to kwh potential.

3 Units producing heat, and the ceiling mounted ones are connected to older less efficient models. 1500kwh seems about right if you kept them at that lower temp. During the real cold weather, I use about that with one unit in a small home and some backup baseboard heat. I'm in a low cost electric area though, my bill was just over $100 last month. I'm staying about even with the low natural gas costs, although paying less in customer fees. I'm comparing apples to apples in my situation and it plays out.
If the installers did honest calculations beforehand, the fact that you have three interior outlets indicates you have a pretty good load to fill.
The people who mention doing really well have super insulated homes, and/or make up the difference with lower cost self cut firewood and similar, especially in regions that have real winters like you and I do.

A/C usage and dehumidifying is where these units really shine. But it may seem like added cost if you never paid for that in the summer time.
The low temperature heat is not super economical compared to the traditional systems.

In your situation, using oil if your old system is still good and you can access cheap oil for now will be as economical during the really cold seasons. End Dec - Beg March. Of course you have to factor the running costs of the whole system into your pricing.

While different for everyone, the economic benefits are more for:
People with small usage needs, where one or two units can suffice, this means a low install cost - a complete system costs $2500. Some installers may charge just as much after install compared to small HVAC system though.
People moving electricity as their only source, to get ride of the service costs and maintenance of other systems. Oil burning systems require maintenance that these really don't.
People in lower costs electric areas, or helping out with in home solar.
People who go DIY.
People who don't have the room or already have vents installed and don't want to tear up the house.

February 2, 2015 - 5:15 pm

Thanks, Bob, for your honest answer. Wish I had known this before I spent $13,000 on this system. With the new electric rate I switched to it says I should save over sixty dollars a month with 1500 kwh, which will bring it back to where we will be saving about $100 month over oil (well, not at this year's oil prices, but "the usual"). My oil system is in very good condition (relatively new furnace) and is easily used - it's spending the $13,000 because I was told I would no longer need it and would save so much that has kept me from using it even with oil down. It only goes on to heat the water and that uses next to nothing.

A question while I have your attention - I was just standing over by the wall unit. There is a big snowstorm outside, it's set high - 76 - and it was blowing ice cold air (was doing that earlier today too but both times went back to warm). We were told this was because we had the fan set to run all the time and it was in defrost mode. Now that the fan is on auto, why is it still blowing cold air? At this very moment it is "resting" as it must feel the 76 ambient has been reached, but it is very disconcerting to go over there and feel ice cold air being blown out!

February 2, 2015 - 6:00 pm

Just a quick look at some of your numbers.

If heat cost $2000 a year before, and now your electric bill in a month in a worst case goes up by $200 for 4 or 5 months, you save $1000 on heat, which is significant.

The cold air question gives me an idea that the installers and sellers didn't explain to exactly just what is happening.
These units go into defrost mode, more often when it is colder and/or it's snowing on the thing outside, which means the unit reverses into A/C mode.
This is to heat up the outside unit to melt the frost/ice forming on it (It's how a dehumidfier works in the summer, because it's outside in 10 degree weather, the condensation freezes). The fan inside is blowing low, but it'll feel like it's on high because it is such cold air. Generally the display indicates this by flashing something or changing an indicator light. It goes back into heating mode when done, and it generally will 'blast' hot air at first to catch back up. You just don't notice the ceiling units doing it as you don't get close to them.
The fan choice has nothing to do with it, when it goes into defrost, it will slow down the fan. You should leave the fan on auto as it regulates itself better. Only if you want the feeling of the air movement should you change the fan speed to high. If you leave the fan on high all the time, you will feel cooler air as the unit will not always be putting out 'high' heat, no different than if you put a box fan in front of you, the moving air will feel cooler.

One benefit if you choose to use it is a more steady indoor temp during shoulder seasons for very little cost, times when the outdoor temp is not so extreme, like fall and spring. These units are highly efficient and run constantly to keep the temp constant. Your mention of not using them in october and having no prior a/c indicates you might be more of the miserly type and not appreciate this or use it. Most Americans want that steady year round comfort and have the hvac system on all year.
You'll be much happier with the A/C experience; it should freeze you out of the house if you wanted it too and provide de-humidification.
The heat is only cheaper compared to the past rising oil costs, which are expected, now is just a blip. Heating at low temps has really only been possible recently with new tech, but it doesn't do it cheaper.

As far as promises and other people's experiences, it can all vary, and the issues are no different than any other industry or product.
Often these units are part of a total green renovation, which involves improving the homes insulation and air sealing, so people include those savings too.
This blog is for people going to those extremes. People who buy windows with higher insulating value than most people effectively have in their walls, and the windows cost the same as the whole wall too ;)

Here is one common sense way to look at your story from afar.
If you paid $2000 a year for heat (sometimes with $100extra payments too), and then paid $13,000 to get cheaper heat, even if the cheaper heat was FREE, that is still 6 1/2 years of heating costs. Obviously the new heat can't be free, and you even mention a rate hike.
Spending a $1000 a year for heat, or HALF is a darn good result, and you seem easily able to achieve that.
Replacing a modern working system is generally not very cost efficient, and I'm surprised your saving as much as it seems.
Honestly you need prior usage numbers and avg temps to make a real determination. As was noted, 1500kwh is not a lot for electric heat only. Your 'feeling' of not as much heat in lower rooms is common for most homes. During bitter cold times, you may have to supplement it. The old oil furnace, likely in the basement helped alleviate that issue.

February 3, 2015 - 12:21 pm

Thanks, Bob, for the defrost explanation - I was told last week by the tech that the cold air was from the defrost mode but that with the fan on auto it would not be blown into the house, and it still is - but now I understand why. He didn't explain that defrost mode meant it was taking care of the outside of the unit- just that it's some (to my mind) mysterious process that happens when it's cold. Now that it isn't so mysterious I understand why there is cold air, why it's colder sometimes than other times, and why even with the fan on auto it has to be blown somewhere.

Yes, the furnace is in the basement and even with the door shut to the "furnace area" obviously heat leached into the room - we didn't always use the baseboard heat because of that. I just didn't think it made such a difference. Also the wall unit in the basement is in the far back corner because there was nowhere else for it and the company said that was not an optimal place for it but they didn't want to put it anywhere else, and so it heats the back but the heat just doesn't flow forward to the rest of the room very well.

We live near the water and so got by without A/C (also have casement windows - yes, new energy efficient ones!: - can't put ugly window units in anyway) but there are always a few weeks every summer where it's unbearable no matter how close to the sea you are. We were very happy with the A/C when we used it, and the dehumidifier.

You're so right, Bob, I am miserly!- (at least with these sorts of things!) but we really didn't need the units in October so I figured, why use even a little energy if you don't have to?

All in all if I just leave the upstairs units on 74 or 76 I am pleased with them and I am hoping that will not make much of a difference in the electricity usage. I am just going to have to make peace with the fact that the downstairs unit is in a bad spot and that when it is very cold out it will reflect in here.

Again, thanks so much for clearing everything up for me. You have done such a good job that I can tell the installers (who were going to come out again) not to bother.

September 18, 2014 - 9:44 am

Hi. I have 4500sq ft 100year old home with new blown insulation. Also having roof replaced soon. Currently have a ETS Steffes boiler that heats our old radiators with hot water. Still find this system expensive. Winter temperatures can get down to minus 20 Celcius some days. Usually minus 10-15 Celcius . Inside the home is not open concept. Many rooms. There are 4 levels of living space. (daughter has a bedroom and bathroom by the attic.). We turn the heat off june 1st of every year and back on sometime in October. I have been reading that a wood boiler may be a good choice for large older homes but just learned about the Mini Splits. Would a mini split be required on each level? What does the cost usually run to purchase a unit . I know if we went with the wood boiler we would only need 1 as it would heat all the radiators. Does minisplits sound feasible in this type of home?


September 18, 2014 - 10:39 am

If looking to do a home HVAC system upgrade/replacement etc, one of the best steps is to get an whole house energy audit performed by a company THAT DOES NOT SELL HVAC equipment.

Often your local utility will refer you to a local company, and many provide rebates. They will evaluate your homes build, equipment, and show you list of potential upgrades, their costs, their payback periods, efficiency, rebates available. Typically they will perform some of the retrofit upgrades like insulation themselves. They should be more customer friendly and able to answer questions, offer opinions, have area expertise, etc.

You'll get a good overall picture and the cost is next to nothing.
Then you can do some research on what they are talking about, or just go with their advice if you are happy. You can ask for quotes from HVAC firms on their recommendations, and also feel you are not getting ripped off as you'll have an idea on the ballpark.
If you are really skeptical, unsure, or don't feel good about them, get another home audit from a different company and compare.

Asking about specific parts of HVAC is like asking about specific pieces of your car without knowing about the rest of how the car operates and how you drive it. You need a good local mechanic to perform and overall evaluation, a mechanic that doesn't profit off of his recommendations.

Nobody online can give you this info without performing such evaluation, and you risk getting bad info or incorrect info if you provide incorrect details or leave off important ones.

September 18, 2014 - 9:43 am

Hi. I have 4500sq ft 100year old home with new blown insulation. Also having roof replaced soon. Currently have a ETS Steffes boiler that heats our old radiators with hot water. Still find this system expensive. Winter temperatures can get down to minus 20 Celcius some days. Usually minus 10-15 Celcius . Inside the home is not open concept. Many rooms. There are 4 levels of living space. (daughter has a bedroom and bathroom by the attic.). We turn the heat off june 1st of every year and back on sometime in October. I have been reading that a wood boiler may be a good choice for large older homes but just learned about the Mini Splits. Would a mini split be required on each level? What does the cost usually run to purchase a unit . I know if we went with the wood boiler we would only need 1 as it would heat all the radiators. Does minisplits sound feasible in this type of home?


September 2, 2014 - 3:03 pm

I am on my third through the wall Frigidair heat pump in my sunroom in the last 25 years.
It is so Noisy. I am planning to switch to a 12000 btu mini split heat pump. Should I go with a Fujitsu or Mitsubishi? The outside unit will be on my pool patio. How high off the ground does it have to be ? Does it have to be shaded from the sun ? Which mini split pump is best value and best track record ? Could I please have an early response if possible. I live in the Midwest with moderate winters. Thank you.

August 15, 2014 - 7:55 pm

We moved to Cape Ann, MA last year and our home is a an 1840s Cape Cod with a new addition. Well insulated. Six rooms, three up and three down. 2000 square feet. Half up/half down. Unfinished basement. We live mostly downstairs and my husband has a small office up. Our master BR is up as well. We have oil fired baseboard and radiators. Our oil bills last winter were ridiculous. Now in the process of having solar panels put on our roof, which will be completed by October. Decided to go with mini splits.
Someone recommended Mitsubishi and I called various contractors to come out. The first guy suggested three units. 2 downstairs (kitchen and living room) and one in our master BR. Of course the compressors will be outside.

I met with a young woman today who asked why I wanted Mitsubishi and I told her someone recommended them. She used to work for Lennox in TX and now works for heat/cool co. that sells both M and L units. She said that Lennox technology allows for the compressor/pump to go into our basement and would cost a bit less than Mitsubishi.
My question is: Any pros/cons to Lennox? Should we only be looking at M or Fujitsu?


August 18, 2014 - 9:33 am

The Mits is a min-split

The Lennox is likely a typical HVAC heat pump system, with indoor ducts, and a cabinet indoors with a larger heat pump outdoors.
If she is speaking of the Lennox mini-split, then it's a re-badged model as Lennox doesn't make them.

Cost differences should be dramatic, but US HVAC outifts over charge on the mini splits to not cut into their core business as much.

Carrier has the most efficient HVAC heat pump system.

August 18, 2014 - 10:02 am

Interesting...definitely want mini split/ductless. So are F and M equal in quality? Mits has the most contractors/dealers near to us.

July 30, 2014 - 9:09 pm

I'm current remodeling a mother-in-law suite that was an addition to our home a year after it was built. (1965) I'm in St. Louis - some what mild winters & hot humid summers. It is not accessible to our main hvac unit. It has it's own gas forced air furnace in the un-heat garage adjacent to the room with a minimum of duct work. To add a conventional A/C unit the outside compressor would have to be on the opposite side of the room as the furnace. We currently cool the room with a window a/c unit. I was considering a mini split in this space. The bedroom and bathroom is about 500 square feet.

My wife was talking to a professional and he said he has had to remove a number of these units and he does not like them. I realize that is very vague. But I have not found many negatives reviews for mini split units. What are the down sides to these units

Thank you for your help.

July 31, 2014 - 6:21 pm

Your situation is perfect for a mini-split unit. However if you have a good functioning central heater system already installed, adding a 1 ton a/c might be economical although not many high efficiency options exist.
HVAC guys don't like these units because they are inexpensive, although many inflate the costs anyway.
Like most humans they don't like change, or prefer to do things as they always have.

You want to use one of the latest models from Mitsubishi or Fujitsu that have low heating ability as they are the most efficient and offer best value for the money. Many HVACs use rebranded models as their main suppliers try to compete in the market.
One month of that window unit costs as much as the whole spring/summer/fall of cooling and dehumidifying will with a mini. It could also provide your heat source cheaper in the mild seasons. It is about equivalent to gas in winter time.

July 22, 2014 - 8:51 pm

Hi. We were recently visited by a representative from a company workibg with MassSave. We are impressed with the idea of the mini-split system. The rep went through our home and told us we would need five units. This is okay too, but the cost is $21,000. The utility company is offering a 0% interest loan, which would be paid over seven years, essentially trading our oil bill for the loan payment for the next few years. We live in Massachusetts, about thirty minutes south of Boston, in an 1895 NE colonial. This all seems to good to be true. Is it? From some of the posts, it seems we are looking at higher electric bills too. Is that the case? We currently have FHA by oil and CA, both are about 14 years old. Thank you for your input! ~Stephanie

November 26, 2014 - 2:47 pm

$21K? How much square footage? My two Fujitsu mini-splits heat/cool 1600 sq ft and cost $6K for both, including installation. I got them for the A/C, but have used them for fall/spring heat, used for heat, electric went up $30 to $50 a month, but oil dropped $330 - a deal. Summer A/C usage was a high of $30 in July/August in electricity. About to do another round of cost analysis.

December 22, 2014 - 8:04 am

Hi Amy, I'm looking for an installer in Southern NH. Who did your install?

July 31, 2014 - 6:11 pm

If you are considering an overhaul, you should get quotes for alternate systems. A HVAC installer will quote you an array of systems. An air source heat pump in a typical HVAC system could be a good alternative as well, maybe geothermal depending on your land and home size.

Obviously your electric bill will go up, but it will be MUCH cheaper than oil.

It often is best to wait until your system is failing to replace it value wise, and focus your $ on other improvements until then. Of course oil prices are starting to make it attractive to not wait in some cases. Air sealing, windows, insulation may be good options. The utility should be able to refer you to a company doing energy audits and retrofits to give you options.

July 22, 2014 - 11:36 am

I have an old Vermont home with multiple rooms we would need to condition.
We have insulated well, and brought our fuel consumption way down. I'd like to install mini-splits to heat/cool the house. Due to the small doorways and typical colonial style, I will need 4 indoor units.
Now, is it more efficient to use a mult- unit model, or 4 individual units. Considering that they all wouldn't need to run at once (especially for cooling).
With the length of the runs to get to 4 units and the size difference between 4 individual units and on big one.. . I wonder which would be more economical to run.



July 23, 2014 - 7:19 pm

A mini-split may not be the right install for a typical American home with typical American history/assumptions.
Also installers are not discounting much if at all compared to typical HVAC systems which can have big discounts, so I would only recommend it if you didn't have old duct work or access for duct work, or really built small and/or tight and were onboard with this approach. If you are thinking any more than 1 or 2 units, you will likely be disappointed unless you really want in room individual control. How often will one room want 66degrees, and the other 78 like adjoining hotel rooms?

As far as multi head systems go:
-The multi head systems are generally far back in the upgrade cycle, and often lack some features on the single head models. Hyper-heat type heating just showed up in the multi-head models. The plumbing can be complicated.
-Efficiency generally trails in the multi-head systems. However this can be hard to accurately figure with how the testing systems can be very different than your final setup. Still, the top efficiency models are not multi-head, as the single head units are where the innovation goes and the big sellers.
-Multi head units in the 2-4 range can cost the same as purchasing 4 separate small single head units; the only issue is having the space for four outside units which is doable if you can house a bigger multi-unit.
-You can't DIY much of the multi-head units, nor can you find parts or much of any online assistance if that is the route you are thinking. Also repairs and parts may be difficult. With separate single head units, you have a backup when one system goes down.

The way mini-split systems cycle, a multi-head unit doesn't really gain in efficiency like you think it would, because a single head unit acts like it were in a multi-head unit and throttles down as needed, and single head units are where the ultra high efficiency systems are.

Your chief decisions in my opinion, after getting some traditional HVAC quotes, even whole house heat pumps like the carrier, is to decide how much heat you'll need with your home type and build. Unlike say many HVAC systems or basic electric heat which is often over sized, if you don't have enough btus for the really cold periods, you will be upset. Electric baseboard and a wood stove could be practical alternatives. You also don't get that instant 'fire' high heat in the cold, so a mini can be undersized and not keep up.

Your typical HVAC has a lot of nice options not in minis, like in duct humidifier, advance filtering packages, integrating HRV/ERV systems, etc. The filter systems in the minis are a joke as far as whole house goes.

July 21, 2014 - 10:24 am

We love our Mini Split Unit. It is eight years old. Other than cleaning the filter we have never cleaned it. I have a chalky white residue building up on the the painted walls in the room and I believe it has something to do with the unit since it is worse on that wall. Also, there are little bits falling out of the unit that look like small moldy pieces of chalk. I wipe the outside of the unit and the slats with Clorox Wipes, but I'm sure I should be "doing something to the inside". I've googled this question numerous times and don't find anything! Help! Thanks.

July 21, 2014 - 12:35 pm

You can use a air conditioning 'evaporator coil cleaner' product.
Try the type that comes in a spray can and sprays foam.
You can find it at any home center store, although you made need to ask someone with actual knowledge there to find the right product as it's not a common use item. Normally only HVAC techs use it as you have to open the air conditioning unit to get access. You want the product that cleans the musty smell from the coils on the INSIDE A/C air handler - that is what they will know it as. You have the same coil system, just inside the minisplit. It's also used on cars with a tool with a long hose that goes into your vents.

You spray it on the metal fins you see inside the unit (just the metal) normally accessible from the top. It generally has a lemon/citrus smell. If you are handy you can remove the front face and spray them from there, but the product is made to settle and self clean so hitting it from the top should be enough. With some units you can easily move the face panel in order to clean the filters.

DON'T SPRAY ANY OTHER CLEANER IN THERE. Clorox and other products can destroy plastics, seals, and the other intricate parts, and corrode metals, and won't work anyhow as you can't wipe the inside. The foam dissolves and washes away the grime, and is made to not damage the other items inside the unit.

It will drain out your condensate line while the unit is running in cooling mode and producing condensate. Normally it is only needed if you have that musty smell from your coils. It won't entirely clean the unit though. The spinning fan blades will still have dirt if they do. You need a tech to disassemble the unit and clean the parts if that is what you desire. You can think of it like a vent cleaning service for typical HVAC systems, only your vent is all in one small box.

This will NOT solve your problem though. What you are seeing is basically a backwash from the air moving through your unit. The air with dust/dirt/etc in it is being funneled from and through that area frequently, thus it collects debri; similar to how grease collects around a stove.
Cleaning the coils will make it run more efficiently (very moderately), but won't solve the air wash issue. The mini split doesn't make dirt/dust/chalk/etc.

It's worth a try for $5 to possibly help the situation. You can't really do it wrong.

May 27, 2014 - 6:42 pm

We had a Fujitsu mini split heat pump installed last fall and it worked pretty wel thru the winter. It heated well and electricity bill is quite a bit lower. The outside unit is 24K Btu and the indoor units are 18k and 9k. Our usage may be a little out of the ordinary in that the smaller unit (9k) is used almost constantly for an out of the way room and we hardly ever use the bigger indoor unit because we heat with wood.
However, it seems like the outside unit cycles quite frequently. One time it bothered me so much I timed it for and hour and a half. It was about 42 degrees. It would go on for 3 minutes and then off for three minutes. This doesn’t seem right to me. Is this normal? In what might be a contributing factor its a 45 foot run between the indoor and outdoor and when the heat is on I can feel heat thru the insulation; its not hot but warm thru the insulation. Would more insulation on the lines help? Could the problem be we have a 24k unit running a 9k indoor unit?
The room (308 square feet) is pretty well insulated. I used to use one of those electric oil heaters to heat the room and normally had it set on either 600 watts or 900 watts. Only when it was 20 degrees did it have to be on the full 1500 watts.


Jack McKee

March 21, 2014 - 2:03 pm

Bob,Thanks for this: "For the A/C in my case there wasn't nearly as much plastic crackling".

At least i have something to look forward to......if we ever get out of winter that is.


March 20, 2014 - 11:57 pm

I have a 9RLS2.Considering it is a bunch of plastic pieces snapped together, it is not too surprising. I was rather surprised when I first mounted mine how flimsy the plastic is, which shouldn't matter much if its engineered properly. Gasketed edges, fewer individual pieces, adding mass to pieces would probably help.It's possible that different tolerances in the mass produced units give people noiser units than others.Also possible that the way the unit is mounted or other stressors could add to it. The mounting bracket is metal so the plastic noises wouldn't come from there.I think different people are more annoyed by it than others, and if you don't locate it near your bed and sleep in dead quiet, you'd never hear it.  The degree of temp swings would obviously have an effect, like constant defrost cycles or how well the area maintains it temperature.You can simulate the noise by going up to the indoor unit, grab both ends firmly and wiggle it, push one side up and side down side, etc.

March 21, 2014 - 8:39 am


Still trying to narrow this down. Its very hard to tell if its plastic expanding cracking/popping or the pipes thermally expanding and contracting making the noise. Padding the inside with foam wrap does definitely help, but still is there. I'm just hoping that the cooling mode is not going to be worse!!!


March 21, 2014 - 9:26 am

The metal piping will ping, like a sonar ping. I would say it's not any more an issue than any other background noise.  I'd guess that part is well engineered and the issue is well understood.For the A/C in my case there wasn't nearly as much plastic crackling, but there was a little more metal pinging. I also noticed more of the in rushing refridgerant whooshing sounds, likely because the fan runs slower/quieter.

March 20, 2014 - 8:13 pm

I wonder if this is an issue with just the Mr slim units. None of the Fujitsu units I am familiar with make anything but a slight guggling when they go into a defrost cycle. Heating and cooling of baseboard hydronic elements always produced ticking noises in my parents house, but a little fiddling with the enclosures usually stopped them. It might be possible to locate what parts are producing the noise in the indoor unit and fiddle with them as Bob suggests.

March 21, 2014 - 8:44 am

Peter, i'm definitely fiddling with this thing.I will eventually get it right even if it means re-plumbing the entire system.

There is no joy or comfort in having a unit that pops/squeaks/cracks while your trying to sleep.That is certain!

I am hoping engineers at Mitsu (or Fijitsu) eventually resolve this for future customers.


March 20, 2014 - 9:56 am


I live in southern NH and have the above Mitsu system installed. Its setup upstairs with about 20' of piping going to outside compressor.The situation i'm having is that the inside unit cycles on/off constantly. It comes on and heats up area, then the vanes go back to a 'parked or level' position and the unit outside makes a whooshing noise which i'm assuming is the defrost cycle. When it goes to heat the area up again, the vanes move to the set position (lower) and fill area with heat. It does this several times throughout the night and is usually associated with what i can describe as a clicking or cracking noise of either the inside unit or the piping. It sounds like plastic is expanding/cracking almost. That noise varies in decible level to barely audible to rather annoyingly loud. Seems to happen constantly when temps are in 30's and hardly at all during lower temps. It's definitely caused loss of sleep. Has anyone else experienced this clicking/cracking noise from the inside unit?The unit itself on the wall can be physically slid up on the wall. It is easily moved up by applying upward pressure on bottom. I was not around during install, but imagine the installation of the unit slides down onto a track or similar. Is the inside unit supposed to have this movement?

I've contacted Mitsubishi and they said to contact installer. Contacted installer and he said the unit can go into defrost cycle whenever it feels like it. Mine seems to go in/out of defrost several times throughout the night. The clicking/cracking is really my issue. I hate the fact that it keeps me from sleeping.

Thank you all,


March 20, 2014 - 2:22 pm

Unfortunately you are experiencing one of the symptoms I would have liked to known about before having bought the unit.The indoor unit is made of flimsy plastic and will expand and contract with heat gain and loss, similar to the pinging of old heat radiators. Because the defrost cycle has a cooling effect, it will be more dramatic around those times. The metal tinging sound is the metal expanding/contracting.If the unit is located in a sleeping quarters there isn't much you can do besides move it.I grew up with metal electric heaters and recognized the sounds right away. It felt like I was inside a submarine during the winter with a constant sonar metal pinging sound. The plastic just pops.If you absolutely can't move it, you could experiment with tinkering with the plastic panels, but it is likely to be a maddening effort with little or confusing results and would definitely kill your waranty.Occasionally I imagine due to manufacturing tolerances a more severe problem may develop; replacing the indoor unit would fix that but it's an expensive gamble, and it might get worse.

March 21, 2014 - 8:36 am


Thank you for chiming in.You describe exactly what i was thinking.The installer came out and padded areas all around to try and stop the cracking/popping.It DID help, but still is there. Unfortunately this is right in the bedroom and moving it is not an option.I'm going to experiment with window/door expanding sealer and report back with results.I've already had very good noise reduction by spraying this foam sealer into the cable / hose covering leading upstairs. The foam virutually elimnated the transfer noise through the pipes coming into the bedroom via the indoor unit.


March 12, 2014 - 9:38 am

Hi Michael,

Wow a blast from the past. I do remember that welder. I'm always amazed at some of the stuff I spent many, many hours building and then never used. Dreams of 60 foot steel hulled boats. Anyway, to your questions:

1. That's an OK calculation, but it gives you an average heating load. In the dead of night the exterior temp will be much lower than during the day, so the heat load will be greater than the average. A house temp set back will help reduce the difference somewhat.Also, your pellet stove probably heating one area of the house much better than other sections so to replicate its performance the heat pump inside unit would need to be in the same general area. If you are going to use the pellet stove as the back up heater when things get really cold then these calculations aren't so critical. I'd probably add 50% to your number.

2. As long as you select a heat pump with an inverter driven compressor, the ones that can vary compressor and fan speed according to demand, the efficiecny stays pretty constant. The benefit from a large heat pump is the higher output at lower temperatures. Note that the the typical family of 9K, 12K and 15K or 18K heat pumps are basically all the same unit with higher compressor and fan outputs. The efficiencies drop a little because the evaporators and condensers have not been increased in size.

3. Minisplits are much more efficienct than window units. The best window units have an EER (Energy Efficiency Ratio) of 11 Btu/Wh. The best mini-splits have an equivalent EER of about 24.  Mini-splits are actually rated by SEER (Seasonal Energy Efficiency Ratio) which is about 115% of EER.

4. Heat pump compressors are fairly quiet, but depending on load a can sometimes growl a little. Mounting on a wall bracket for the most part will be OK for a well built, well insulated wall. However, I recommend a ground mount on a tall secure stand with good shielding from snow. Vibration from the compressor can be transmitted through the refrigerant lines so keep the lines no shorter than 15 feet.

This winter has been a good test for my 4 year old 3/4 ton Fujtsu mini-split. I sold my old woodstove so the only other heat I have is electric resistance heaters (if I care to use them, NOT), passive solar gain and the excess energy from my solar hot water system. What I usually do in the dead of winter is turn the temp down to 62 at night when we turn in. The house will slowly coast down overnight and if its around 0 or above in the A.M. the house will be right around 60-62. That's downstairs. Upstairs its a few degrees cooler. The heat pump is puttering along delivering warm air at a moderate pace. If it has gone down below 0, like -10, the heat pump is still working, but only putting out luke warm air and the house will be down around maybe 58. I set the temp back up to 68 and as the outdoor temp rises the heat production climbs and everything warms up. Having the compressor on the east side of the house where it sees the sun early helps. I certainly dress up with a good sweater, (thanks pres Carter), but even on cloudy days that little 3/4 ton unit brings the house back up to 68. Yes my house temp cycles and yes I making use of the thermal mass characteristics to work with the heat pumps abilities. This works very well and on sunny days when the passive gain and excess solar thermal energy take over I shut the heat pump off.

March 20, 2014 - 11:31 am

Peter.. Thanks for much for the great followup info!  I'm working with Sam Zuckerman up here in Maine.  His company is Maine Solar Solutions.  Really like working with him.  He did my gridtie PV array too.

Thanks again and if you ever find yourself up around Harpswell, would love to take you for a sail and talk alt energy. 


March 9, 2014 - 11:04 am

Hi Peter!   Wonder if you remember me.. I bought an old VW engine-powered welder from you sometime back in the early 1980s.

I now live in Central Maine in a 2500 sq ft saltbox I built.  Its pretty energy efficient and I heat with 1.5 to 2 tons of wood pellets/year. 

The house has no backup heat and I'm looking to make a mini-split my primary and the pellet stove the backup.  This article, and the discussions here, are just about the best I've come across, thanks!  I do have a few questions for anyone who can help.

1. Did I do this BTU calc correctly (based on Peter's formula above)?  2 tons of pellets, @ 70% efficiency appears to be 23m BTU.  Average annual total degree days for Waterville, ME is 7261 (5 year avg).  23m/7261 = 3168 BTU/degree day for my house.  Avg degree days per day in Waterville for January (our coldest month) is 44.  3168*44/24 = 5808btu/hr.  Does this sound right? 

2. Does it hurt to oversize a unit?  Will this improve low-temp performance?  We've been close to or below zero almost every night for the past month.

3. Are heat pumps more efficient at cooling than a windows A/C?

4. If the outside unit is mounted on an outside wall, will it transmit much vibration into the wall?


February 18, 2014 - 2:53 pm

Well the day is finally here.  My unit is going to be installed on Weds.  My question, is I currently have standard thermostats throughout my zones in my house.  How do I regulate the hydronic in floor with the heat pump to maintain both a warm floor with the heat pump?  Is that possible?  Do I not want to do that?  I am only installing one 12RLS2H on my main floor that is 1760 sq ft and I am going to run the in floor in the basement.

I was thinking I would just set my house to 55 deg for the in floor and then set the heat pump to 65 deg.  If the heat pump can't keep up the in floor would kick on, but I don't think that would be very efficient as it takes the floor so long to heat up.

Do I need to buy new thermostats with a floor sensor?  Do those exist?