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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August 6, 2020 - 9:21 am

Hi, I have an unfinished basement at my cottage on posts with 2 walls open to the outside. Could I install the outside compressor in the basement with the control heat/cool portion inside the cottage. Only use 3 seasons not through the winter. Thanks

May 29, 2020 - 11:15 am

I've been having what I think is short cycling from the Mitsubishi wall units in my bedrooms. The rooms have all been renovated with most of them getting closed cells spray foam and all of them getting plenty of attic insulation. Theoretically each wall unit can throttle down to 2000 BTUs but since the three bedrooms are all connected to one multi-head outside unit they're restricted to what that unit can go down to, which is 6,000 BTUs. If I set the temperature to 70° on a humid day the wall unit pretty quickly gets the temperature down to that but the humidity stays high or it creeps back up pretty quickly. If I switch to dry mode it gets rid of it fast but it gets pretty cold pretty quick. It's a hassle to keep swapping back and forth between modes but not sure what else to do. I have a separate outside unit which does the main living area. I don't have the problem out there because I think the demand for that unit is higher so by the time it gets the temperature down it's taken care of the humidity. I've tried putting the fans on the lowest setting hoping that it would take longer to reach temperature and therefore remove more humidity but not a lot of luck there.

April 15, 2020 - 2:54 pm

i just got a mini split. installed it myself. started in the spring heating season. i tried to keep the fan speed low. but doing this the indoor air handler would pop and crack. you have to keep the fan speed up in heating mode. so expect the sound of air...moving. i had to set my fan to auto. i'm guessing in cooling mode it will be quieter. but that seemed to relieve the popping noises. 

February 23, 2020 - 2:36 pm

our question is can the entire unit be mounted in the basement of a very very old house?  the basement is not airtight, has a huge earthen berm on one end - with cut granite stone walls surround - and a small room with low ceiling & cement floor with french drain for water to run out - would it act as a dehumidifier & heat unit in the old cellar & allow for ac or heat? in rooms above? house is summer home no heating / ac system in place

January 24, 2020 - 10:19 am

I did not get an answer to this question: I have been told that leaving a mini split on 68 degrees overnight costs less than turning it down to 60 degrees or turning it off completely and letting the oil heat keep the room at 50.  Does this have any basis in fact?  For how many hours off would it make sense to turn it off versus leaving it on 68?

January 23, 2020 - 3:20 pm

If you have a woodstove backup, then it's not your sole heat source, which is probably good. It's my understanding that they can have some trouble keeping up in very cold weather, so the woodstove is a great idea.

January 23, 2020 - 3:05 pm

Did you receive an answer? I am wondering same thing. Thank you

January 16, 2020 - 9:44 pm

Is it unwise to have a Fujitsu mini-split as primary heat source and only a wood stove as a back up?  Live in Southern Vermont.

January 8, 2020 - 1:28 pm

I have been told that leaving a mini split on 68 degrees overnight costs less than turning it down to 60 degrees or turning it off completely and letting the oil heat keep the room at 50.  Does this have any basis in fact?  For how many hours off would it make sense to turn it off versus leaving it on 68?

December 18, 2019 - 9:04 am

yesterday my mini split was running about 6 degrees above the setting,today when it's a couple of degrees warmer it is running about 6 degrees below and seems to be blowing cool air is this normal?

November 30, 2019 - 12:55 am

Any information would be so helpful. I have 2 mini splits. Daikin brand. They pop, crack, and make so much noise that I get startled.  The loud pops and cracks happen more frequently as temperature drop below 25. The banging (sounds like plastic expanding ) happens at any temp. Please someone advise what is causing this so I can help the hvac company try to remedy. They say this is normal. This is so disturbing that I spent 8k on these 2 systems. I can’t imagine this is normal. It wakes me at night and startled my guests when they are over. The fan is pleasant and quiet. The defrost mode of gushing is fine also. It is the bangs and cracking and popping. Please advice. 

November 11, 2019 - 2:40 pm

Massachusetts has a "solarize" program to encourage the installation of these systems. I currently have an oil furnace heating my nearly 100 yr old, two story, 6 room home. My current water heater works off of the oil furnace, and that uses oil all summer.Will using the mini-split and heat pump water heater, reduce the temperature in my basement so much that my pipes would be endangered?  Would I be better off with a solar water heater than the heat pump in terms of basement temps?  Also how does one determine how many units will adequately cover the house? Do you need units in each bedroom upstairs or will air flow to each of the rooms? There seem to be a lot of variables here. Any answers to these questions, and any thoughts on other questions that I should be asking before making a decision would be appreciated. 

April 28, 2019 - 12:54 pm

What is the recommended and most economical mode for heating--"AUTO" or "HEAT" in 20-50F temps? Installers recommended AUTO 24/7.

January 31, 2019 - 1:34 am

Home cold.not warming up.5units. Temp about 6 degrees.never had these issues,either steam heat.or forced air?

November 15, 2018 - 6:09 pm

Just installed A 1.5 TON MINI SPLIT HEAT PUMP FROM MR. COOL  I'm a retired HVAC guy with very little experience with heat pumps.  I just have to say that l am impressed!  I ordered a system with no resistance heat.  Right now, here in Vermont it is 24F, and the unit is kicking out 130F.   I'm curious to see how low this thing can go!

October 24, 2018 - 10:09 am

My dining/kitchen is 1 is 12 ft wide by 20 ft long...
My living room is next to it with wall and door opening 6 ft wide.
Living room is 12 ft wide by 17 ft long!
I can mount unit 12,000 mz-na mistubushi between the kitchen and dining room on wall almost directly accross from the living room door opening.
My question is will heat /ac go from wall to living door opening which is 12 ft away and heat /ac the 12 by 17 ft living room without cold spots etc?
I only want 1 unit to do this do to cost!
My house is new ranch and well insulated...
I like this location as no air would blow on me while sitting in my easy chair and noise from unit and compressor is in kitchen\ dining room where I spend very little time,90% of my time is sitting in living room watching tv!

October 5, 2018 - 9:23 pm

I am rebuilding a 1300 sq ft house, and trying to make it carbon neutral. The house is in the bay area of California, and the summers are not very hot, and winters not that cold. All the outside walls are being insulated with R13. A trick for the attic is to put insulation under the roof with radiant guard, for support and radiant blocking, to prevent the summer heat from baking down into the house. Then a little air flow keeps the house cool. There is also insulation under the floor, and double pane windows.  A heat pump water heater has been installed in the garage. These need a place to dump cold air, and a source of warmer air. The old gas furnace was past it's last leg, so I threw it out, along with all the ducts, and gas pipes. Now the task is to replace it with heat pumps. 
    I figure mini-split ductless heat pumps is the way to go for highest efficiency. Heating a 2000 sq ft house with gas peaked at 70 therms per month around December. That comes to about 68 KWH of heat per day. The sun doesn't provide much solar PV juice in the winter, so I conclude that a high COP is essential.  Searching around for quite some time, I find that there are engineering documents typically called Engineering_Guide, like for Daikin 2-3-4MXS_Engineering_Guide.  Search for Capacity Table may help.  This is a lengthy document, that has among other things Capacity Tables. The capacity tables show output BTU/hr, input watts, for various conditions. Daikin is very extensive, showing outside units vs. combinations of inside units vs. outside temperature vs. inside temperature, vs heating or cooling. I am very impressed with the detail! 
   Looking through the guides for Mitsubishi, LG, Daikin, and Fujitsu, I conclude that Daikin has the best combination for my re-build. Not each vendor provides the same detail as Daikin.  Sizing studies indicate that the typical sizing depends on the need to heat up the room in a reasonable time, not on the rate of heat leakage. This becomes more true as the insulation is improved. So a high COP is desired during the warm-up time, as well as the maintain time.  I have not found the COP under the maintain conditions, where the system slows down, and cycles on and off. But, at least then, the power level is not so high. Still 1000 watts for 24 hours is the same as 24000 watts for 1 hour on the bill. 
   Anyway, after all that background, I see that Daikin can give me a COP of greater than 5 for standard heating conditions of 43F outside, and 70F inside, with the 4MXS36RMVJU  when lightly loaded with CTXS07LVJU or FTXS09LVJU, except when all 4 outputs are used. I could not find any conditions that the other companies promised such high performance in heating mode.  A COP of 5 would reduce the worst power requirement from 68 KWH (heat) per day to 13.6 KWH(electric) per day. It starts to look as if a solution exists! 
    The trouble I'm finding is that Daikin dealers are not well represented in my area. They have a reasonable amount down south, but not here. Here Mitsubishi is highly used. I see that I can buy the material on the web for reasonable amounts. But, reading the warranties, I see that no company will warranty units sold to non-professionals, and they use the purchasing details to make that determination. That's somewhat understandable given the difficulty of attaching the line-sets properly.  I fear that to prevent leaks in heating mode, the 30 atmosphere 120F (MOL) condition of the line sets make proper sealing and reliability a precise assembly requirement.  I also hear that not all line sets are the same.
   So my question, how do I get a good installation where the support and expertise for Daikin is slim, and likely very few installers have been installing for the purpose of heating - regardless of the equipment involved?    

July 17, 2018 - 8:34 pm

Hi, right now I have one furnace for my 2 unit house  I want to condex the two units to sell one and live in the other until my boys graduate college  I need to have two separate heat systems to be able to condex it  my house has forced hot water old radiators as my house was built in 1872  what is the least expensive way to separate the two units heating  

January 15, 2018 - 11:14 am

had new 12000btu lg mini split installed outside temp has been around -14 to -20 degrees Celsius which is between 7 and -4 degrees f I have ran unit at 30 degrees Celsius for 24 hrs straight and can only get room up to 18 to 19 degrees celsuis is this normal I own  a mini home whick is 16 ft by 70 ft inside unit is in living kitchen which is open concept measure 26*16

December 16, 2017 - 5:00 am

I have never seen an inside unit installed 18" from the floor. Anywhere. But it totally makes sense. Why have I never run acriss yhis while I was doing my research on heat pumps? Nothing in any of the information I read from manufacturers addresses this. And all installs I've ever seen are done closer to the ceiling. I will bring this up with my provider for sure.

December 16, 2017 - 4:54 am

I've had my LG Mini Split for 2 winters now and it gets really cold here (-30° or more). The heat pump's efficiency drops proportio ally to the temperature. But I take the breakers out for my electric baseboard heaters in May and I haven't yet put them back and temps have dropped below freezing. I will use convective heat transfer heaters upstairs (flat panels you mount on walls yourself and plugs in 110. Amazon has them Amaze-Heater) and those can be switched on as required. I was told to leave the heat pump temp on at least 21°C and as high as 27-29 in the winter to make it more efficient. So far do good. I have a 45 yr old 3 bdr 2 story end unit townhouse that needs insulation/new windows/doors. But I love my Heat Pump. A/C is also amazing.

November 11, 2017 - 12:51 pm

I have four units in my 1850 cape. 1 unit upstairs two on main floor and one in the basement. I also use a Harman pellet stove on main floor when it gets really cold. I got rid of the oil and furnace. With the Harmon I can set it for a temp. And same with the heat pump. If one shuts down the other comes on. The heat pump will also help in circulating the heat from the stove. Heat pump in basement keeps floors summers it dehumidifies. Last year I used dehumidifier in whole house which kept it cooler also.

April 20, 2017 - 8:35 am

i am installing a minisplit system, maybe a Gree model, approximately 18,000 btu. , or mitsubishi.

i would like to install just one of the 2 indoor units now ,but i am told that both must be installed to use the system.

this does not make sense since you do not have to run both inside units all the time

one of the indoor uits is 12,ooo and upstairs is 6000btu.

March 22, 2017 - 8:21 pm

Who knows the pros and cons of each

February 28, 2017 - 11:51 pm

The Efficiency Manager.................................I have owned my heat pump for 8 years and it has performed well......except for when the really cold frosts............ we have here in the winter. It can then be hesitant at say 6 degrees centigrade below. 

After watching a Youtube video to-day....I now wonder why I didn't enquire about reducing the effects of the cold with some sort of shelter previously. I would appreciate any comment you can give me in this regard.

Thanks in advance..............RAay Kirton.....................

December 12, 2016 - 7:17 pm

I have an LG split system . Air conditioner works great. Heat system works great till outside air temp drops to freezing then it just throws cold air. Is this normal?

December 10, 2016 - 3:09 am

hi there. I live on a moderate climate, with winters almost never reaching below 32F at night. I have a high temp Daikin heat pump, the one that has two circuits to increase the temperature in two stages, but it's not a resistor on the second phase; a different gas I am told. It heats up the water which circulates the house's radiators.
anyway, I was wondering what the most efficient water temperature setting is for this device. 40c, 45c? 50? 60? etc.. I would appreciate any advice.

December 8, 2016 - 6:40 pm

I am posting this to educate and clear the BS about the mitsubishi hyper heats being "super silent" as they advertise.

In cooling mode, granted the ONLY thing you will hear is a gentle whisper of air coming from the blower. Ahhh sweet silence.

Now fast forward to winter.
The first season i had these MSZFH12NA's running i thought there was something seriously wrong.
I called and had the tech's come out, but what is happening is actually normal according to the technicians and Mitsubishi engineers.

Here is the problem:

When it gets cold, below 32 degrees cold, the variable speed motors in these things REALLY start ramping up.  When they do, the lineset carries that vibration from the increase in RPM's into the house. Where the lineset goes through the wall there is a 'pinch' point   directly onto your wall framing. The vibrations travel from the outside unit, up the lineset and into the wall radiating through the wall. If you have one of these and its cold outside you WILL HEAR IT. The way i can best describe is that it sort of sounds like a car idling outside with RPMs frequently going up and down. Sometimes its loud, then it drifts off. Regardless you will hear it unless you're deaf.
I was able to somewhat deaden the sound by repositioning the lineset "looser" inside the line-hide pvc they use to make it neat looking. My installers had ziptied all the cables tightly together creating one big vibrator. I clipped them and loosely back together. It made a difference. The lineset is insulated, so that helps, but not smashing them all together also made it not as noticeable to me.

My regional new england mitsubishi rep actually confirmed they know about these issues by saying that Mitsibishi engineers are working to create a "muffler" system that will hopefully eliminate this buzzing/vibration.

Both my systems are installed correctly as recommended by Mitsubishi. Or in other words NOT attached to wooden structure of the house. One system is on a pedestal, the other is hanging off my basement concrete foundation. One was installed in 2013 and the other in 2015. They are "new". I like them in winter, but LOVE them in summer. 

I'm sure that some will say they never hear them at all. The one i hear every night is below my bedroom on the 2nd floor.
Laying in bed at night when its nice and quiet, you WILL hear this if its closeby.

Hope this helps!

November 22, 2016 - 11:28 pm

I've been researching mini-splits and think I may have at least a possible solution for those noicy units that keep cycling on and off.  An important factor when installing a unit is to ensure that there is an adequit flow of air.  If the sound of your unit cycling on and off is an issue consider moving the thermostat further away from the unit:  And keep your doors open to let air flow into other areas.  Your issue could be partially caused by your indoor wall unit over powering the size of your room.   One HVAC engineer that visited my home suggested I needed three wall unit including a 9,000 btu unit in my children's 9' by 7' bedroom.  While I'm just a home owner doing his research!  I'm suggesting you have to think for yourself even when the experts sound like they know what they are talking about.  Good luck!

May 5, 2016 - 11:03 am

Hello Peter,

I am building a small house for a customer and would like your recommendation on which brand and size min split to purchase.

The house is 24 x 26 with a very open floor plan. There is a 10 x 20 open loft area. 

The framing is double 2x4 walls with 1.5" between walls, hence 8.5" exterior walls with dense pack cellulose. Rafters are 2x12 filled with dense pack, not vented.

Cathedral 18' ceilings. The home features 3 - 6' sliders and 3 - 6' wide Anderson casement windows.

Thanks you for your help.

David McCullough

August 13, 2015 - 12:33 pm

1. We've had a few assessments for a mini split installation in a master bedroom/ensuite. Some have recommended a 9000 BTU unit, the others a 12000 BTU, so we are a little confused. Here's our scenario:

369 sq. ft., a third of which has a vaulted ceiling and the remainder normally 8 ft. ceilings. Six energy efficient vinyl windows, one of which is south facing. As for climate, we are in Nova Scotia, so summers not too hot (except for a couple of weeks maybe) and winters similar to New England states for temps.

The house is 25 years old and reasonably well insulated. The room has one interior wall, two exterior brick walls, and one wall with vinyl siding. Heating for the rest of the house (basement and main floor) is supplied by ETS units, and air conditioning is not usually necessary for those floors.

What size would you recommend?

2. We're considering either a Mitsubishi Mr. Slim or the new Fujitsu model. A bit leery of the latter, as the reviews don't seem to be very good. Any thoughts?


August 11, 2015 - 8:48 pm

Hello Marlynn,

Before you think of changing your heating system I would suggest you get an energy audit done on your home and make some improvements. Any house that is not well insulated is going to be hard to heat comfortably with mini split heat pumps. Just as you probably experience some discomfort in the house as it is now, the same situation will exist with any other heating system. I would first improve the air sealing of the house. I would then look at increasing insulation levels. Finally I would consider making up simple double layer window insert panels to double the R value of you windows. Once you have made these improvements Then take a fresh look at mini splits.

Yours, Peter

August 11, 2015 - 6:22 am

We own a house in the Northeast U.S. that is approx. 175 years old less than 2000 sq. ft. of living space. It is not well insulated, and part of the house is log. We have heated it using a pellet stove on one side of the house, while using electric heaters on the other side (primarily to keep pipes from freezing in the winter months) with occasional use of a propane stove and an oil furnace used as back-up or to warm the house when we have guests here. We are now looking at replacing all of the above with one system. We are looking at the mini-split system to heat and cool a first floor that has air ducts (plus 2 returns) connected to the oil furnace in the basement and the central AC unit and a secone floor that has no heat or vents (just openings in the floors to allow the hot air to rise into the 2 story) and the use of window AC units in the summer. There is an attic that does have insulation, as well. As we are currently working through quotes from a number of local HVAC businesses, a recent contracter suggested a heat-pump system in the basement with a new oil furnace to back-up the system is the temp. drops, a second heat-pump in the attic and vents placed in the ceilings of the second floor. The contracter prior to this contractor suggested a mini split system with a unit (heat coil and fan) that would utilize the air ducts under the first floor and individual wall mount units in the second floor rooms (3 units would be needed). There would be the possibility of installing a second mini-split in the attic, if the first floor unit would not be enough. I would appreciate any opinions as to which system would be the better for an old house and more cost efficient. Thank you!

July 19, 2015 - 8:31 pm

I'm building a 200 sq. ft. tiny house (TH) out of SIPs in SE Michigan to park at a year-round campsite with 30 amp service. I was considering a mini-split largely for A/C though, considering we don't need cooling very often (10-30 days/year), I was leaning toward a portable to save $$. However, if I could both heat and cool my TH with a mini-split...

If you wish details to calculate possible BTU's, my TH interior, is 26' x 7.5' x 10' with about 82 sq.ft. of windows and door, and 4.5" SIP walls (~R-16).

Average lows in January are 15 degrees F, but can go to -20 (Brrrrr!). I must be careful about anything "supplemental" because of the limited amperage at my campsite and non-vented propane could be lethal, or at least would pump way too much humidity into the TH.

I would greatly appreciate your expertise.

Thank you,

May 11, 2015 - 2:08 pm

This winter was our first with our units. We live in northeast Ohio so our temps were in the negatives quite a bit. We have a gas fireplace upstairs and the contractors forgot to put a gasoline in for our lower level but we do have a wood burner in our 4 season room which he
Per immensely. We had difficulty keeping the temps bar able on the main floor so the contractor is putting in our gas line so we can have another gas fireplace for those extra chilly days...that's solving our winter problems but now it immediately skipped spring and we've been dealing with upper 80's so we have the air on upstairs and have the shades closed and fans on downstairs. It seems to be good but I don't know if that is a good thing or if we are supposed to keep all 4 splits on the same temp. Please advise as my husband kes telling me to leave the intros alone and stope adjusting them all the time...

April 29, 2015 - 11:48 pm

We put in a Mitsubeshi small duct heat pump and a heat pump hot water heater this February. Previously we started installing great windows. We are about to install a new roof, foam insulation. In other wards we are trying very hard to be very conscientious with our energy use. We were also told we would see a significant reduction in our energy bill. Our bill doubled! Tonight it occurred to me that the hot water heater is putting out cold air after it removes the heat to make the hot water and the ductless is the constantly having to warm up cold air. Does that seem like a reasonable conclusion? If so what can we do? We spent about $20,000 on this system. Also the ductless has ultraviolet light to kill bacteria mold etc. it was one of the top reasons it appealed to us. Could it be increasing our kWh so much. We used 1000+ over last year for March?

March 13, 2015 - 9:53 am

It is very important that during the heating season to not set the remote or thermostat to "auto" setting.
Use the "heat" setting only. By using the "auto"setting you are asking the unit to maintain the selected temperature. So it will do what it must to maintain that temperature you selected even if it has to cool the room down at times. I never use this "auto" setting.
As far as gurguling is concerned.....most problems stem from poor installation. Either there is too much refrigerant or not enough. Were the lines purged well and was the vacum left on long enough?
It is important to follow the manufacturers table for length of line set and adjust coolant as necessary.
Hope this helps.

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