EcoRenovator - View Single Post - New to heat pumps -- questions

mincus · 12-04-11, 08:45 AM

Hello all,

We bought a 25 year old two story about a year ago now. It has two air source heat pumps, one for upstairs (about 800 sq ft) and one for the main level (about 1200 sq ft).

Overall, I'm pretty happy with them. It's an all electric house, which I was worried about buying in the first place. I thought my bills would be through the roof. However, one year in, my highest bill was around $130. And that was during one of the coldest months we've had in St. Louis in quite a while. Lowest, in spring and fall was around $55. So, I can safely assume heating is costing us around $80 for the coldest months. Considering our old house (900 sq ft) cost about $100 to heat with natural gas, I'm pretty happy.

However, after a year in, I'm starting to try to look for some savings. I've already insulated fairly well (but could always do more).

I'm thinking of a simple change, but I don't know what kind of effect it could have. I have been thinking lately about the times I'm running the heat pump. We are comfortable with a temp of 66 when in the house. However, it seems hard to try to keep that temp overnight upstairs during the very cold nights. Last year, I would let upstairs drop to around 60 during the day, then kick it up around 6:00 so it would be comfortable when we went to sleep. On cold nights, the heat pump ran often ran all night.

Would I be better to run the upstairs heat pump from about 2:00 to 5:00 (usually the warmest time of the day) up to about 72? Then, just turn it down to 66? I've tried this a few times this year so far. Being that it's not too cold yet, it works well. The heat pump hasn't turned on overnight at all. These were with overnight lows of mid 30s. However, it will be a different story when the temps get colder.

The main floor heat pump I'm not as concerned with. The temperature doesn't fluctuate as much because it mostly only has the walls to lose heat to (instead of the roof like upstairs). Plus, downstairs I can turn the heat pump down at night and up in the morning.

I guess basically it comes down to: does the increased efficiency during the day override the increased heat loss due to a higher temperature differential between inside and outside? I know this has to do with amount of insulation, outside temp, and probably numerous other factors, but are there any general ideas I can go with here?

One other question. I had an HVAC guy out to fix something else. I asked him when to turn on emergency heating. He told me at 32. This didn't seem right to me. My experience is that the heat pump can keep up down to around 17-20. Is it too hard on my heat pump to run it at those temps, or as long as it is keeping up, am I alright?

Any help is appreciated.

Thanks!

12-04-11, 08:45 AM	#1
mincus Helper EcoRenovator Join Date: Feb 2009 Location: St. Louis, MO Posts: 42 Thanks: 0 Thanked 0 Times in 0 Posts	New to heat pumps -- questions Hello all, We bought a 25 year old two story about a year ago now. It has two air source heat pumps, one for upstairs (about 800 sq ft) and one for the main level (about 1200 sq ft). Overall, I'm pretty happy with them. It's an all electric house, which I was worried about buying in the first place. I thought my bills would be through the roof. However, one year in, my highest bill was around $130. And that was during one of the coldest months we've had in St. Louis in quite a while. Lowest, in spring and fall was around $55. So, I can safely assume heating is costing us around $80 for the coldest months. Considering our old house (900 sq ft) cost about $100 to heat with natural gas, I'm pretty happy. However, after a year in, I'm starting to try to look for some savings. I've already insulated fairly well (but could always do more). I'm thinking of a simple change, but I don't know what kind of effect it could have. I have been thinking lately about the times I'm running the heat pump. We are comfortable with a temp of 66 when in the house. However, it seems hard to try to keep that temp overnight upstairs during the very cold nights. Last year, I would let upstairs drop to around 60 during the day, then kick it up around 6:00 so it would be comfortable when we went to sleep. On cold nights, the heat pump ran often ran all night. Would I be better to run the upstairs heat pump from about 2:00 to 5:00 (usually the warmest time of the day) up to about 72? Then, just turn it down to 66? I've tried this a few times this year so far. Being that it's not too cold yet, it works well. The heat pump hasn't turned on overnight at all. These were with overnight lows of mid 30s. However, it will be a different story when the temps get colder. The main floor heat pump I'm not as concerned with. The temperature doesn't fluctuate as much because it mostly only has the walls to lose heat to (instead of the roof like upstairs). Plus, downstairs I can turn the heat pump down at night and up in the morning. I guess basically it comes down to: does the increased efficiency during the day override the increased heat loss due to a higher temperature differential between inside and outside? I know this has to do with amount of insulation, outside temp, and probably numerous other factors, but are there any general ideas I can go with here? One other question. I had an HVAC guy out to fix something else. I asked him when to turn on emergency heating. He told me at 32. This didn't seem right to me. My experience is that the heat pump can keep up down to around 17-20. Is it too hard on my heat pump to run it at those temps, or as long as it is keeping up, am I alright? Any help is appreciated. Thanks!