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

Before changing your heating system, consider getting an energy audit and making home improvements. A poorly insulated house will be difficult to heat with mini-split heat pumps. Improve air sealing, increase insulation, and add double-layer window inserts to enhance comfort. Then reassess mini-splits. Thanks for the valuable advice!

Might be a good idea Maureen--it sounds like you are unsure the heat pumps will be able to keep up.

I have heat pumps and oil heat for water only.  I will be excessively cold this week-end. Should I turn on oil heat to keep pipes from freezing in cellar where I don't have heat pumps?

My haier heat pumps are great for a/c in the summer. They are less efficient for heating and I have a gas furnace. Is it ok to just shut them down. 

I have installed a heat pump hot water heater along with 2 1ton mini splits in the basement.  What are the tricks to keep the mini splits operating in the 1 st stage, instead of trying to keep up with the hot water heater?  The min Mr. Cool DIY temperature is 62 degrees.

Bob Hatch

Turners FaLLS, mA.

13764 A

If you own a mini-split heat pump system, you probably already know about the benefits of efficient heating and cooling, zone temperature control, and quiet operation. Mini-splits require little maintenance and are easy to operate. To get the most out of your mini-split heat pump system, check out these seven tips to maximize it’s efficiency, lower energy costs, and enhance your comfort during the summer months.

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.

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.

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.

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.

We installed a Bryant mini-split heat pump system in our hundred-year-old house last Spring. For the cooling season, the system was fine. In Fall, we changed to heat and had no problems. We have a gas-fired boiler and cast iron radiators and we brought those online around Thanksgiving. The mini-splits, trying to keep up, ran our electric bills way up, so we left them on but turned their thermostats down to 62. Now it's bitter cold, and the old radiators are doing their job. Our electric bills, however, are still a problem. They came down somewhat, but are still higher than they were before the mini-splits were installed. Should we turn the units off entirely?

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?

I recently installed mini splits that are working fine in temperatures of high 20s to above 40. We live in Michigan so the weather can get quite cold. We will be leaving the house on occupied for the winter months of January through March. I'm wondering if I should leave the heat pump on low for that period of time or turn them off and use the electric baseboard heat

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

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.

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. 

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

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?

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

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.

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?

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?

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. 

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. 

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

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

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!

My dining/kitchen is 1 room..it 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!

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?    

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  

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

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.

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.

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 warmer..in summers it dehumidifies. Last year I used dehumidifier in whole house which kept it cooler also.

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.

Who knows the pros and cons of each

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.....................

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?

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.

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!

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!

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

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?

Thanks.

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

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!

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,
Michelle

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...

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?

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.