# Heat pump idling while your wood stove is running?



## jimcrook (Dec 10, 2020)

Forgive me if this is a dumb question. My primary heat source for my small house is an electric mini-split heat pump. When I am operating my wood stove (sometimes all day, sometimes for just several hours), I typically just turn down the thermostat on my heat pump (to about 60 F) so that it's kind of idling while the wood stove is cranking out heat. My thought being the heat pump will be ready to heat the house in the middle of the night when the wood fire dies down. But am I wasting electricity by keeping the heat pump on?  Should I just turn it fully off?


----------



## Tron (Dec 10, 2020)

Your thermostat keeps the heat pump off (at least the energy-hungry parts like the compressor and fan), so it's just in standby. That doesn't really use much energy.


----------



## Dataman (Dec 10, 2020)

How I run mine with Pellet Stove.   HP set for 68f.   Never comes on because hallway is 74f.   But it's there to pickup the load incase of failure  of stove.   24f transformer is all that is running.  Since today is above 33f already HP will pickup the load until 3pm.


----------



## jimcrook (Dec 10, 2020)

Tron said:


> Your thermostat keeps the heat pump off (at least the energy-hungry parts like the compressor and fan), so it's just in standby. That doesn't really use much energy.


Good to know. Thanks!


----------



## peakbagger (Dec 10, 2020)

Yes there is some parasitic loss when its idling but not much as long as you have it in automatic fan mode. Of course you could set the timer on the remote and just have it turn on in a few hours and save the idle loss for a few hours.  its a nice match, in cold weather they struggle to bring a space up to temp but they are good at keeping it at a set temp.


----------



## begreen (Dec 10, 2020)

Parasitic loads can be high if there is a compressor heater on the system. That can be like 80w. This is enabled on some systems and optional on others. It lets the system crank out warm air on startup when the temps outside are below a preset temp.

FWIW, I don't mess with the thermostat at all. If the heat pump needs to come on while the woodstove is burning, so be it. It can help convect the heat to the farther reaches of the house but this is with a whole house ducted system.


----------



## Crisputer (Dec 10, 2020)

I'm heating with wood to save money in the long run so I turn the power off at the breaker myself but I'm in SE TN plus the wife is home during the day to keep it warm so that's what works for me. We're on our fourth season this way in a typical 1,200 sq-ft ranch.


----------



## DBoon (Dec 11, 2020)

I just set mine and forget it. If the wood stove cools down and the house cools down, the heat pump will just come on automatically.


----------



## Brian26 (Dec 11, 2020)

begreen said:


> Parasitic loads can be high if there is a compressor heater on the system. That can be like 80w. This is enabled on some systems and optional on others. It lets the system crank out warm air on startup when the temps outside are below a preset temp.
> 
> FWIW, I don't mess with the thermostat at all. If the heat pump needs to come on while the woodstove is burning, so be it. It can help convect the heat to the farther reaches of the house but this is with a whole house ducted system.



This is correct. Almost all decent cold climate units heat the compressor when its idle at low temperatures. Mitsubishi actually uses the compressor windings to preheat the compressor by just energizing it with 50 watts. Its necessary when you want to start your unit when its -5 out. It similar to a block heater. I have read its mainly because liquid refrigerant will settle at the coldest lowest spot which is the compressor.

This is from the Mitsubishi hyper heat service manual.

10-1. PRE-HEAT CONTROL
If moisture gets into the refrigerant cycle, or when refrigerant is liquefied and collected in the compressor, it may interfere the start-up of the compressor.
To improve start-up condition, the compressor is energized even while it is not operating. This is to generate heat at the winding.
The compressor uses about 50 W when pre-heat control is turned ON. Pre-heat control is ON at initial setting.


----------



## Brian26 (Dec 12, 2020)

jimcrook said:


> Forgive me if this is a dumb question. My primary heat source for my small house is an electric mini-split heat pump. When I am operating my wood stove (sometimes all day, sometimes for just several hours), I typically just turn down the thermostat on my heat pump (to about 60 F) so that it's kind of idling while the wood stove is cranking out heat. My thought being the heat pump will be ready to heat the house in the middle of the night when the wood fire dies down. But am I wasting electricity by keeping the heat pump on?  Should I just turn it fully off?



What brand and model do you have? I have always been fascinated how these units operate. I have read a ton of service manuals and documentation.  All the manufacturers openly publish all their documentation including the service and technical manuals.  Mitsubishi has an entire website with public access to all their stuff.

It seems that all the manufacturers will cycle the blower at very low speed for a min or two to sample the return air. They use extremely reliable and energy efficient resin packed  brushless DC motors in the indoor and outdoor fans. The indoor fans only consume like 80 watts at full speed.  Just set it and forget it. It will kick on when it needs to.


----------

