Minisplit for heat at high elevation and cold temps

[folivier]

My cabin is at 9400' elevation in Colorado and has a wood stove + electric baseboard heaters. Our cabin is basically open downstairs with open loft bedrooms upstairs. Electricity is pretty expensive using the baseboard heaters so I've been thinking of upgrading to another source. Options are propane forced air but that would require a large tank installed and the heater which would be over $10,000 plus the tank rental and installation cost. Another option is a pellet stove but that would be to replace the wood stove and still requires daily attention. We winterize the cabin when we leave in the fall and turn on the electric heat before we leave home for our 2 month winter trip so it's about 50º when we get here. That way we can turn on the water and fire up the wood stove.
We do burn lots of firewood mainly aspen since it's basically free.
Mitsubishi minisplits have the heat pump working down to -22ºF. Our lowest temperatures in winter are usually around 0ºF. The efficiency goes down once you get below freezing ambient temperatures and at our altitude efficiency is also lower. But even if I'm only at 60-70% efficiency the electricity useage is still 1/2 or less than the baseboard heaters. And the heated air should circulate better than what the ceiling does on low. The cost of a 36,000 BTU minisplit would be around $3000 so much less than other options and I can install it myself. Mitsu comes precharged with freon so I'd just need to pull a vacuum on the lineset once installed. I'd keep the baseboard heaters and wood stove in case the temps are extreme.
My question is: is anyone using a minisplit for heating in low temperatures? How well is it working?

 

[Franklin]

My cabin is at 9400' elevation in Colorado and has a wood stove + electric baseboard heaters. Our cabin is basically open downstairs with open loft bedrooms upstairs. Electricity is pretty expensive using the baseboard heaters so I've been thinking of upgrading to another source. Options are propane forced air but that would require a large tank installed and the heater which would be over $10,000 plus the tank rental and installation cost. Another option is a pellet stove but that would be to replace the wood stove and still requires daily attention. We winterize the cabin when we leave in the fall and turn on the electric heat before we leave home for our 2 month winter trip so it's about 50º when we get here. That way we can turn on the water and fire up the wood stove.
We do burn lots of firewood mainly aspen since it's basically free.
Mitsubishi minisplits have the heat pump working down to -22ºF. Our lowest temperatures in winter are usually around 0ºF. The efficiency goes down once you get below freezing ambient temperatures and at our altitude efficiency is also lower. But even if I'm only at 60-70% efficiency the electricity useage is still 1/2 or less than the baseboard heaters. And the heated air should circulate better than what the ceiling does on low. The cost of a 36,000 BTU minisplit would be around $3000 so much less than other options and I can install it myself. Mitsu comes precharged with freon so I'd just need to pull a vacuum on the lineset once installed. I'd keep the baseboard heaters and wood stove in case the temps are extreme.
My question is: is anyone using a minisplit for heating in low temperatures? How well is it working?

Well I have 5 Mitsu splits. One in master bedroom, 2 in large living room, 1 in guest room and one in a garage /exercise area (my house is 6K feet and also has 3 other HVAC groups that largely stay turned off cause the splits do the job). SO, i can tell you they are a great choice. BUT, I don't live in a super cold region. Worst case is below freezing for a few weeks and super hot in the summer. (Southeast region). Never had any problems and the cost is about what you quoted. You might need 2 in your place depending on your sq footage. Ive found they do not drain your electricity as much as a normal HVAC system (which is why I normally keep the main system off). I can only tell you they have been performing well.

 

[OfficeSpace]

An article recently published in The Colorado Sun does not address elevation, specifically (and Boulder is about 4000' lower than your cabin), but offers references that might be worth pursuing (perhaps the author gained insight or leads while researching?).

My guess is thinner air reduces efficiency while lower boiling point increases efficiency; as CoP ratings don't reference elevation, perhaps the difference is negligible. Regardless, I recommend avoiding thermostat setbacks!

Edit: How much are mini-splits really affected by altitude? addresses this in terms of Btu/h.

 

[folivier]

I did find a couple charts that show efficiency loss at elevations, Fujitsu and Mitsubishi, and it ranges from 70% to 81% efficiency compared to sealevel.

 

[427Vette]

I own 7 Mitsubishi mini splits between my cabin, shop and house. I am in northern MN so it gets cold but no elevation to speak of. I have gas boiler floor heat in all of these buildings along with wood heat if I need it so the mini splits are not my only source of heat. However I have played around with turning the floor heat off and just running the mini splits for several days just to see how it would work in case I ever needed to heat that way. They work absolutely fantastic even in below zero temps. I wouldn’t hesitate to put one on your cabin.

 

[Samsung4321]

-8 °C

My question is: is anyone using a minisplit for heating in low temperatures? How well is it working?

My latitude is 35° S, altitude 600 m, winter minimum -8 °C, summer maximum 42 °C, insulation R4 ceiling, brick open cavity plasterboard walls.

My reversible circuit air conditioner heat pump delivers heat more cheaply than alternatives.

The indoor unit is mounted high to produce good vertical air circulation in summer and to maximise space at floor level.

Winter vertical air circulation is less resulting in increased vertical air temperature stratification.

We reduce the vertical temperature stratification with a box fan on its back slightly elevated from the floor to 'scoop up' cool air near the floor and 'shoot it' vertically to mix and displace the warm air near the ceiling. Substantially reduces vertical temperature stratification.

In a predominantly heating climate mounting the indoor unit near the floor would lessen vertical temperature stratification. A fan to push warm air from ceiling to floor in winter would further reduce stratification.

 

[folivier]

Looking at various units it seems that I may be better off with 2 18K units rather than a single 36K, SEER values appear to decrease with the 36K units.
No problem with having 2 separate units if higher SEER, that would give me better control of temps.

 

[Out of Steam]

Looking at various units it seems that I may be better off with 2 18K units rather than a single 36K, SEER values appear to decrease with the 36K units.
No problem with having 2 separate units if higher SEER, that would give me better control of temps.

Redundancy is good, as is not trying to heat and cool areas on two different levels with the same unit.

You might also look up and see what the actual heating capacity for the heat pumps is at the design minimum temperature for your altitude and area. At your high elevation a 99% design temperature would appear to be about -10ºF.

https://farm-energy.extension.org/wp-content/uploads/2019/04/7.-Outdoor_Design_Conditions_508.pdf

For reference, the 36K BTU ducted heat pump in our 1900 SF house in Virginia would only keep up alone to 27ºF. Though, the house isn't well-insulated. I understand that mini-split capacity holds up better at low temperatures.

You could also leave an electric baseboard or two in place (which I see you mention) at the locations nearest your plumbing, with thermostats left lower than the heat pump(s), to make up any low temperature capacity shortfall. They would also recover your temperature more quickly after a power outage.