Propane or electric heat pump

[jwstewar]

I've got a heat pump, but instead of a the electric heat strips we have a propane furnace to function as "back-up." Works exactly the same as the strips (too cold or move the thermostat more than 3 degrees) but is just a normal furnace. BTW, I have our outside thermostat set to 30 degrees before we go to the propane furnace. I talked Mom & Dad into installing a heat pump this summer as well as a new natural gas furnace. Don't know how it is doing yet as a heat source (cooling was good) but they just found out Monday there was a problem with the install and it was running the furnace instead of the heat pump. The installer has since corrected this mistake, so we'll here shortly. They replaced a 35 year-old natural gas furnace and a 220v room AC and a 110v room ac unit. Their electric bill went down quite a bit just from the cooling standpoint.

[Bird]

Jim, I'm surprised to hear that their electric bill went down. I always thought the window unit air-conditioners were more energy efficient than the central units. I'm in a total electric house so no gas furnace. I actually prefer total electric, although the gas may be a more economical alternative. I did recently install a 230volt window unit that both heats and cools in my 21' x 25' shop building, but I got it in just as the summer and high heat ended and so far it isn't cold enough to need the heat, so I've only tried it on cooling one day and heating another. It does a good job, but I don't know what it'll cost.

[jwstewar]

I think it went down because it was able to keep everything cool by cycling vs. the 2 window units running all of the time and still not really able to get the house cool.

[Pat]

Jim S. I think you have your outside thermostat set a bit low. Unless you have a very non-standard heat pump you are probably switching to gas at too low of a temp. Freon based heat pumps lose efficiency below about 40 degrees fairly quickly. I'd be amazed if you get better over all efficiency with the cut over point set as low as 30F. Of course if your electricity is super cheap compared to your gas prices I suppose it is theoretically possible.

I have the latest Lenox technology with Freon 410. The units are 19.2 SEER. Taking into account the comparative rates for electricity vs gas, the combustion efficiency of the furnace, and efficiency of the heat pump our break even point is 38F.

We have been having temps in the 80's and 70's after a sample of cold weather gave us our first two light frosts. It was in low 60's at 0700 a couple days ago but only 40 this AM. Eventually we will have a winter and then I can find out how well all this gas backed heat pump stuff works. There is so much variation in temps day to day that the in-floor hydronic isn't such a perfect fit. We can have heated forced air in place of or along with the hydronics to avoid afternoon overheating till the weather cools off.

[img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/smile.gif[/img]

[jwstewar]

The first year or so w/ the outside thermostat it was set for 35. We went through a lot of propane that year. I adjusted down to the 30 and cut our propane bill dramatically while not really noticing a change in the electric bill.

We just installed a new 12 SEER Air-Flo - made by Lennox - this summer. Prior to this we had a 10 SEER Coleman-Evcon. So far the Air-Flo seems to put out a lot warmer heat than the Coleman did and it doesn't run near as much even in the 40 degree weather. The installer said he had one customer w/ his outside thermostat down to 14. I think this might be low, but the installer said he had most cusomters between 30 & 40 w/ most at 35.

[Pat]

Jim, 14F????? An air to air heatpump won't do squat to "mine" heat from 14F air.

I am a great believer in reality over theory. When carefully observed reality clashes with theory, the theory needs to be improved.

By the way, what are you paying for electricity?

Oh, did you by any chance check the outside thermostat with a calibrated thermometer? That could easily be the source of 5-10 degree error.

I'm glad that you have reduced your energy costs. Once apon a time I was the energy conservation officer of SUBASE but they drummed me out of the corps when I refused to sign a statement about letting the bastards freeze in the dark.

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[jwstewar]

Not sure what the total cost is. When we were looking at replacing the heat pump this year due to hail damage I called AEP and tried to get the straight of it. They make it confusing now due to deregulation (thank you politicians you really helped me there) between generation costs, distribution costs, and transmission costs I forget. What I do remember though, is we get a break on our first 800 Kw something like Nov. - Apr. Then it goes up to the "regular" rate.

As far as calibrating my outside thermostat I haven't done so directly, but I've compared it to my little digital thermometer in the kitchen that also reads outside temps. About the only time I really see any discrepancy is early in the morning and the digital one says it is 40 something (sun shining on it) and the furnace is still running vs. using the HP (it is still in the shade). Most of the time (like night time temps) they seem to be pretty close.

[Pat]

jwstewar, Sounds like your outside thermostat is definitely "Close Enough." That was one possible source of error but apparently not in your case. It is getting cold enough this week to start to get some realistic experience with our new installation. My wife reminded me that I need to close up a hole between the inside of the house and the space between the front porch roop and porch ceiling. We cut an access hole but I haven't finished building and installing the door yet. This is on the north side of the house and the wind is gusting to over 40 from the north and temps headed below 32 soom. Bet you can guess my next project.

All I can say is this had been the shoulder season. It has been weeks since we needed heat or A/C. Oh well...

[img]/forums/images/icons/smile.gif[/img] Pat [img]/forums/images/icons/smile.gif[/img]

[chrisjbell]

I'm (as usual) chiming in kind of late... [img]/forums/images/icons/blush.gif[/img]

Heat pumps are great until you hit temps below about 40ish (as mentioned in some of the other posts). I don't know what your weather is like where you live but if you have cold winters I'd say skip the heat pump and do propane.

The other issue you can get with a heat pump is that when it gets really hot the cooling isn't anything like you get with a dedicated AC. I live in CA now and a heat pump might make sense here, but I had a heat pump living in Indiana and was cold in the winter and hot in the summer.

However, I did not have any of the fancy backups that I've read about in this thread. I just had the "whatever the builder installed" heat pump system.

[jwstewar]

Funny we are still talking about this. I've been thinking something didn't seem quite right with the new heat pump. It got down to 15 last night so we should've switched over to the furnace. I noticed thought that the heat wasn't as warm as usual with the furnace and the thermostat wasn't blinking the little "flame" to indicate it was on back-up. The air was quite a bit warmer than normal heat pump air at 15 but not the propane furnace air. I look outside and the outside unit is running. I've come to the conclusion some how they must have the whole system wired up wrong on the back-up. It seems like it is running both the heat pump and the furnance. So we are now running two system and cooling the "hot" air from the furnace so that it isn't as efficient as what it would be by itself. [img]/forums/images/icons/mad.gif[/img] [img]/forums/images/icons/crazy.gif[/img] Needless to say first thing I did at work this morning was give them a call to get out there and get it fixed. They are supposed to be there at 3:00 today.