Comments on: How the Heck Does a Heat Pump Get Heat from Cold?!

By: Paul Rohrs

Paul Rohrs — Fri, 13 Jul 2012 20:02:01 +0000

Well stated information!
Well stated information!

By: Noreen

Noreen — Wed, 09 Feb 2011 21:45:39 +0000

Ok, so all this talk of heat
Ok, so all this talk of heat pumps and yes we have one here at our 1978 Apt building...HOW do we go about telling management and or Corporate, that these things are old ..I mean OLD...the coils are all bent inside (the apt) we have ONE ceiling vent for the LIVING,DINING And Kitchen area..(which is placed above sliding single door) I have cleaned the inside coils with a soft brush and has helped some! BUT geesh louise, these run forever! I will set thermastat on 65 and it will run for 2 hrs? or more? IS this NORMAL?

By: shaun phillips

shaun phillips — Fri, 21 Jan 2011 01:49:10 +0000

My past electric bill was
My past electric bill was $211, which is for a small basement apartment in DC. I thought that seemed high until I realized I had a heat pump and that raising the heat from 60 to 68 each day is not economically wise.

I am now keeping my thermostat at 68 degrees during the day and night. My question is if it's common for the heat pump to come up regularly during the day (handful of times each hour) to keep my apartment around 68 degrees? I am worried that it comes on too much.

Also, is it really that costly for me to turn up the heat only one or two degrees during the day if I need it warmer? I worry that even adjusting the thermostat slightly, will result in high heating bills.

Thanks,
Shaun

By: Allison Bailes

Allison Bailes — Tue, 18 Jan 2011 17:14:31 +0000

Ginny, I think when you say
Ginny, I think when you say 'supplemental,' you mean 'emergency,' right? Doesn't the thermostat setting you had selected for December say 'emergency heat'? The only time you want to select that is when your heat pump is not working. In other words, if you have the thermostat set to 'heat' and the house doesn't warm up at all, then you use 'emergency heat.'

Heat pumps cannot keep up with the heating load in most houses when the temperature gets below a certain point. They have built in supplemental heat to add to what the heat pump does. The supplemental heat is electric resistance heat, which is not very efficient.

If you're using it only to supplement the heat pump, that's not so bad, but when you set the thermostat to 'emergency heat,' you're bypassing the more efficient heat pump and using only the strip heat. That's why your bill was so high in December.

By: Ginny

Ginny — Tue, 18 Jan 2011 09:08:35 +0000

We live in OH and just
We live in OH and just received our Dec/Jan all electric house bill.It shocked us, $507. Never that high in 5 years. Called my electric co. and was told to turn off my supplemental heat and just heat the house by heat pump. My furnace man told me to switch to supplemental when below freezing, so I had the supplemental switch on for all of December, Hence the high bill. Will it hurt my furnace or the heat pump to just run the heat pump without supplemental heat when the weather is below freezing? I can't affort another bill like that! I do not want to damage this furnace, it's about 40 years old. It's a Trane. Seems to be warm enough in here, i keep it at 68 degrees. Need your imput, thanks, Ginny

By: Allison Bailes

Allison Bailes — Sun, 26 Dec 2010 18:33:14 +0000

Kempf42, I don't really know
Kempf42, I don't really know anything about integrated heat pumps & HRVs, but it seems like I heard something not long ago similar to what you're saying - that they're a good idea in theory but don't work so well in practice.

Thanks for the link to your blog. I checked it out, and it looks like you've got an interesting project going there. It also reminds me of when I was building nearly a decade ago and having to make all those decisions about products, materials, and methods. It takes a lot of work and research to do it right, and even then it's still difficult. Keep up the good work!

By: Allison Bailes

Allison Bailes — Sun, 26 Dec 2010 18:21:38 +0000

Bill, you've got a lot of
Bill, you've got a lot of good questions, and I'll be writing another article soon to address them. For now, though, let me give you a brief answer. Heat pumps can still pump heat down to at least the single digit temperatures Fahrenheit, possibly even below zero, because the boiling point of the refrigerant is down around -50°F.

As to when the supplemental heat kicks in, there's something called the 'balance point,' the temperature at which the house needs exactly the same amount of heat that the heat pump can move into the house. When the temperature goes lower than that, you need supplemental heat. That temperature is usually in the mid-30s F but depends on the climate, the equipment, and the house. It's hard to imagine that your equipment/house has a balance lower than 11°F, but if it does, then yes, the supplemental heat shouldn't come on.

Look for more on this topic soon.

By: kempf42

kempf42 — Wed, 22 Dec 2010 07:52:12 +0000

Good explanation of the basic
Good explanation of the basic thermodynamics behind heat pumps.

I’m in the process of an energy remodel and at the beginning we considered a ground source heat pump for our hydronic heating system, and a new air handling system for air conditioning. As we were planning also on having heat recovery ventilation (HRV), I thought we could get an integrated air handling system that would both ventilate and cool. Unfortunately, it is not to be found in the US (though they are available in Europe).

On top of this, the system required a large (80 gallon) buffer tank to hold water either chilled or heated to avoid having the pump switch on and off frequently. Our moderate climate in CA would not have the heat pump running all the time. The reason they need this is because the pump motors are not robust enough to handle modulating action, and tend to age more quickly if they are run in that mode.

Both of these, plus the high price, convinced me to stay with our gas fired hydronic boiler. It generates fossil carbon but I’ll just have to buy offsets for it (much as I dislike the idea of offsets).

If you want to know more about our energy remodel, check out the blog: http://netzerolife.blogspot.com.

By: BillGriz

BillGriz — Wed, 22 Dec 2010 06:35:44 +0000

Thanks for the excellent
Thanks for the excellent explanation. My question is "how cold will a heat pump still be effective?" I recently built a new house and had 2 13 SEER/7.8 HSPF units installed. They both have electric heat strips for backup. I've heard a lot of different numbers (temp) that a heat pump can operate at. Some claim that heat strips kick in automaticaly when temps get into the uppper 20s, some don't kick in automatically at all. The other night temps got down around 11 degrees(f). The thermostat never indicated that heat strips came on (emerg. heat). System ran almost continuously but kept the house at selected temp of 67. At 11 degrees outside, was the system still operating in heat pump mode or was it most likely on backup? How low can a heat pump go?? I understand that the heat producing capacity diminishes at lower temps.

Thanks,

Bill

By: Kimberly Wagner

Kimberly Wagner — Sun, 19 Dec 2010 00:18:32 +0000

Thanks so much for your help!
Thanks so much for your help! I had the heat pumps installed several years ago when my HVAC units needed to be replaced, and as far as I know I don't have a separate gas furnace, but I'm not getting any heat from either the upstairs or downstairs heat pump, so I must be wrong about that...must be tied into a gas system in some way. This'll teach me to put off reading the mail! Thanks again for your reply. I just discovered this site and I think it's a great resource!