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Old 12-11-2019, 11:09 AM   #1
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Heat pump limits?


Would a heat pump be able to get the house temperature to 50 degrees without the use of the built in heat elements if the outside temperature is 25 degrees? Thanks
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Old 12-11-2019, 11:22 AM   #2
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Re: Heat pump limits?


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Would (an unnamed/undescribed) heat pump be able to get the house temperature to 50 degrees without the use of the built in heat elements if the outside temperature is 25 degrees?
1) Turn the power off to the strip heaters.
2) Wait for the next 25F day/night.
3) See what happens.
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Old 12-11-2019, 11:24 AM   #3
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Re: Heat pump limits?


depends on heat loss characteristics and capacity of heatpump. easiest way to test is to do what was suggested above.

50 degree return could be too cold for the heatpump and the outdoor coil could get starved of refrigerant.
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Old 12-11-2019, 11:37 AM   #4
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Re: Heat pump limits?


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depends on heat loss characteristics and capacity of heatpump. easiest way to test is to do what was suggested above.

50 degree return could be too cold for the heatpump and the outdoor coil could get starved of refrigerant.
Just asking because I'm a snowbird & will be heading south shortly & while away I plan on setting my thermostat temperature to 50 degrees. I do have heat elements installed but was curious if they would be need in 25 degree outside temps. Thanks
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Old 12-11-2019, 12:52 PM   #5
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Re: Heat pump limits?


i don't think 50 degrees would be good for the heatpump - i would say 62 minimum.

the return air temperature impacts refrigerant pressure and if it's too low it may not work properly - just like running in cooling mode when it's too cold outside can cause problems.
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Old 12-11-2019, 06:23 PM   #6
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Re: Heat pump limits?


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i don't think 50 degrees would be good for the heatpump - i would say 62 minimum.

the return air temperature impacts refrigerant pressure and if it's too low it may not work properly - just like running in cooling mode when it's too cold outside can cause problems.
Would I be doing harm to the system setting the temp at 50? Thanks
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Old 12-11-2019, 06:31 PM   #7
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Re: Heat pump limits?


Very low return air temperature can negatively impact the way the refrigerant cycle works and cause it to run inefficiently, not pick up much heat from the outdoor air.

Edit: It can also cause problems defrosting.

Just set to at or above 62f. (even that can be too low) It's not made for a 50F return air temp.

Not a question of damage, there's no point of setting it that low when doing so won't save much energy.
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Last edited by user_12345a; 12-11-2019 at 06:39 PM.
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Old 12-12-2019, 05:32 AM   #8
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Re: Heat pump limits?


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Would I be doing harm to the system setting the temp at 50? Thanks
Yes. It could cause liquid flood back to the compressor. Could also cause some oil logging of the indoor coil.
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Old 12-12-2019, 06:38 AM   #9
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Re: Heat pump limits?


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Yes. It could cause liquid flood back to the compressor. Could also cause some oil logging of the indoor coil.
Interesting info. You would think they would let people that buy these heat pumps in on that important info.
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Old 12-12-2019, 08:40 AM   #10
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Re: Heat pump limits?


You could also just put it in emergency heat mode and set it just to keep pipes from freezing I would say 50 would be just fine. When you return warm the house using emergency heat until you get it to around 66 and then turn the heat pump back on.
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Old 12-12-2019, 08:51 AM   #11
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Re: Heat pump limits?


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You could also just put it in emergency heat mode and set it just to keep pipes from freezing I would say 50 would be just fine. When you return warm the house using emergency heat until you get it to around 66 and then turn the heat pump back on.

With this new info that might make sense. The thing is I thought using the heat pump without having to use heating coils was the real advantage as far as energy use goes. I thought a heat pump was supposed to be much more energy efficient than heating coils. If I do as you suggest I will be defeating that purpose of energy efficiency.
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Old 12-12-2019, 09:22 AM   #12
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Re: Heat pump limits?


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With this new info that might make sense. The thing is I thought using the heat pump without having to use heating coils was the real advantage as far as energy use goes. I thought a heat pump was supposed to be much more energy efficient than heating coils. If I do as you suggest I will be defeating that purpose of energy efficiency.
You are correct about the efficiency, however as has been pointed out allowing the return air temp to go below a certain limit is not good for the system for several reasons. To ignore this is to invite potential problems that could be very costly, much more so than the cost of electricity. Heat pumps are designed to maintain temperature not wild fluctuations. When you return and set the thermostat to normal what ever that temp may be, the resistance heat is going to be activated anyway to supplement the heat pump (unless you shut it off). In that scenario you are paying for the heat pump and the resistance heat until the thermostat is satisfied or close to satisfied. With my suggestion you just pay for the resistance heating.

I don't know your electric rate, the efficiency of your unit, how well your home is insulated and so on. So I am just going to assume that if you are gone for 3 or more days and your home is reasonably insulated you probably won't get that many calls for heat set at 50. You may break even using the resistance heat to re warm the home, or probably even be ahead just because you were not using the heat very much for the time you were absent. If you stay away long enough it is a no brainier. At any rate I would much rather pay the electric invoice than a repair invoice
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Old 12-12-2019, 09:28 AM   #13
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Re: Heat pump limits?


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You are correct about the efficiency, however as has been pointed out allowing the return air temp to go below a certain limit is not good for the system for several reasons. To ignore this is to invite potential problems that could be very costly, much more so than the cost of electricity. Heat pumps are designed to maintain temperature not wild fluctuations. When you return and set the thermostat to normal what ever that temp may be, the resistance heat is going to be activated anyway to supplement the heat pump (unless you shut it off). In that scenario you are paying for the heat pump and the resistance heat until the thermostat is satisfied or close to satisfied. With my suggestion you just pay for the resistance heating.

I don't know your electric rate, the efficiency of your unit, how well your home is insulated and so on. So I am just going to assume that if you are gone for 3 or more days and your home is reasonably insulated you probably won't get that many calls for heat set at 50. You may break even using the resistance heat to re warm the home, or probably even be ahead just because you were not using the heat very much for the time you were absent. If you stay away long enough it is a no brainier. At any rate I would much rather pay the electric invoice than a repair invoice
We will be away for 5 months. So if I put the system to emergency heat only, I will be losing the benefit of the heat pump efficiency for all 5 months.

Last edited by dommm; 12-12-2019 at 09:32 AM.
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Old 12-12-2019, 09:40 AM   #14
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Re: Heat pump limits?


Yes, However if it were me I would set the thermostat on EH for 40 degrees to minimize the call for heat. This will also insure you have no frozen pipes and water damage. Or you could set the thermostat to 66 and enjoy the benefits of heat pump efficiency along with a higher electric invoice. Remember any system is most efficient when it is not running.
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Old 12-12-2019, 10:06 AM   #15
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Re: Heat pump limits?


Frozen pipes are not an issue for me, we turn off our pump (well water) & drain the pipes. The only issue we have with the house freezing is that the plaster walls (old house) start cracking. If not for that I would just shut the system off while we are away.
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