Heat Pump question

[Wild Turkey]

LOML was talking to her best friend about house we are building and friend strongly suggested we consider Propane as the "back up" heat source instead of heat strips.

We will have propane for the "emergency" heat source but I hadn't thought of it as a heat pump secondary source.  

Anyone have a heat pump with propane as the secondary heat source?

Here in KY electricity is cheap (but will that last with the "anti-coal" forces at work?) and with fairly mild winters I'm wondering if it's a good idea?

Any suggestions?

[fredhargis]

I've had 3 systems like that, the first I had installed almost 30 years ago. It sounded nuts when I first heard about it, but worked out so well that the subsequent 2 systems I had installed were done the same way. The first was a Trane air source heat pump with their LP gas furnace. these are called "split systems" and unlike strip heaters, only one heat source works at a time. So with the Trane I had set to cutover temp to 30º, which is to say when it dropped to 30 the furnace came on and the HP was turned off. Then when it warmed back up the HP would cut in at 30º, I had set it that high because with an air source HP the house always felt cooler with the HP running even though the thermometer showed the same temp. Anyway, we moved about 10 years ago and I put a new system in that house. This time it was a ground source HP (geothermal) and an LP gas furnace. This was Carrier, and it worked the same way...you only had one or the other running...but the cutover temp was 10º, and the switch back occurred at 15º. So then we moved again 4 years ago and this house had  geo HP with strips. The previous owners actually turned off the breaker to the strips due to the high cost....and these folks had money! With strips, the HP runs all the time, and the strips kick in to supplement it on the colder days. So I had this system replaced as well. Again went with Carrier since I was so happy with the last system, and got a geo HP with LP furnace. The operating system on this unit is slightly different...you don't set a cutover temp. The system senses (somehow) when the HP is providing enough heat and cuts over to the furnace automatically. So far this has worked extremely well. BTW, with the geo HP the house doesn't have the "cool" feeling when it's doing the heat. So my advice to you would be the same as your friends, go with the gas furnace. I agree with your sentiment about the cheap electric, and the warmer temps...but remember, it only takes a small generator to run the furnace if you lose electric. So I'd still get the gas furnace.

[R Clark]

Here's my experience:

We had a heat pump with electric strip auxillary backup.  The compressor on the heat pump cratered in January 2018.  Since it was 14 years old and not particularly efficient, we went with a new heat pump and aux unit.  This time, though, we replaced the electric strips with a propane burner since we have a 1000 gallon propane tank.

Big reason we went with the propane aux:  The whole HVAC system can be powered with a reasonably-sized backup power generator.  When the old system failed, I was getting ready to upgrade the backup generator from 7KW to 22KW.  The electric strips were powered with a 60amp circuit, and that was too much for a regular household backup power generator.

If I had to do it again, and this is one of my big regrets, I would have switched to geo-thermal when I replaced the whole unit.  But I got in a rush, and just did the easy thing.  I have the perfect property for geo-thermal, a well-insulated house.  Since I was already spending $10K for a new HVAC system, I probably could have had geo-thermal for an additional $10K.  However, tax credits could have reduced that cost, and the remainder of the delta would have been quickly amortized.

[aquaticjim]

I have a geothermal heat pump and I live in Southern Michigan.  My system has the electric emergency heat.

Although I have not performed a detailed search, does any manufacturer of geothermal heat pumps offer a propane emergency heat?  I know you can install two separate units but that is complex and expensive.  If there is a manufacturer offering propane as a backup, are they high efficiency as in 95%?

[fredhargis]

I have a geothermal heat pump and I live in Southern Michigan.  My system has the electric emergency heat.

Although I have not performed a detailed search, does any manufacturer of geothermal heat pumps offer a propane emergency heat?  I know you can install two separate units but that is complex and expensive.  If there is a manufacturer offering propane as a backup, are they high efficiency as in 95%?

I don't see them as any more complex than the strip systems (maybe Blackhat can chime in). Gas furnaces are fairly simple and (more importantly) very reliable.

[MKepke]

i have a dual zone system with a HP plus strips downstairs and propane heat upstairs.

My opinion largely mirrors fredhargis’ - propane provides a more pleasant heat than the HP at really low temps (such as they are in central NC).

That said, I like having diversified systems and sources of heat. If something konks out or you have supply problems, you always have heat.

I remember one year the propane co
company had problems making deliveries due to a cold winter and a broken pipeline. I think I paid $3.40/gal that year.

-Mark

[blackhat]

The current front runner for a system replacement in my home is an air source heat pump sitting on top of a 2 stage high efficient furnace.  I'll use an outdoor temp sensor to shut down the heat pump and switch to low fire gas heat, the internal timer on the furnace would engage high fire when required.  My heating season is considerably longer than most of you and I have a higher heat load because of the temps we see.  In the milder climates many of you have, a single stage high efficient with a heat pump would be reasonable.

[Roly]

The current front runner for a system replacement in my home is an air source heat pump sitting on top of a 2 stage high efficient furnace.  I'll use an outdoor temp sensor to shut down the heat pump and switch to low fire gas heat, the internal timer on the furnace would engage high fire when required.  My heating season is considerably longer than most of you and I have a higher heat load because of the temps we see.  In the milder climates many of you have, a single stage high efficient with a heat pump would be reasonable.

Just curious at what outside temperature do you switch over from the heat pump to furnace ?   Roly

[JosephP]

The current front runner for a system replacement in my home is an air source heat pump sitting on top of a 2 stage high efficient furnace.  I'll use an outdoor temp sensor to shut down the heat pump and switch to low fire gas heat, the internal timer on the furnace would engage high fire when required.  My heating season is considerably longer than most of you and I have a higher heat load because of the temps we see.  In the milder climates many of you have, a single stage high efficient with a heat pump would be reasonable.

That is what we have.

Used to switch to gas at 34.  I bumped it up to 40.

[blackhat]

The simplest conversion process would be to remove the existing air handler section and replace it with a furnace and the appropriate coil.