From the Washington Energy mailbag: heat pump vs. propane

“I’ve been reading your articles on heating and cooling with a heat pump vs. AC with great interest. Being from Northern Nevada and now living in Graham, WA, I’m rather suspicious of heat pumps. My wife and I just bought a house that needs renovation which includes replacing the heat pump. I’m used to the traditional furnace / central AC systems. I don’t understand how running a 230 volt, 30 amp compressor all the time along with electric heating coils is more efficient than propane. When I do a cost comparison of BTUs I find that propane generates 91,000 BTUs per gallon. To convert electricity to BTUs there is a multiplier of 27x the current electrical rate per kilowatt hour. This equals approximately $2.50 per gallon for electricity as opposed to currently $1.59 per gallon of propane. In this vein, propane is much cheaper to us. Plus when the power goes out, I can’t heat my house, whereas if I had a propane furnace that runs a simple 110-volt blower, I can plug into a small generator and be toasty. I don’t see where electric only is such a good advantage. I would think multi-fuel would be a better advantage to cost and survivability. Please help me out where I may be wrong.” – Roger in Graham, WA

Roger, thank you for the comment. It is clear you have done a tremendous amount of research into this and are very well versed in the same types of comparisons we look at. We use a slightly different approach, where we apply various “costs per unit” of energy (kwh – electricity, gallon – propane, therm – natural gas, etc) to equations that factor in equipment efficiency to get all the choices on the same page of “cost to product one million BTUs of heat”.

One of the challenges with propane and oil is that they are free market commodities that can swing pretty wildly from one year to the next. If you can consistently get propane around $1.59 per gallon, that certainly makes that a strong contender, as you have outlined.

Electricity and gas are obviously regulated, so they are a bit more predictable over time. That being said, it certainly warrants a full look at any given situation to get the full picture.

As a starting point, a heat pump is generally preferred in this area over just propane, oil, or electric resistance heat due to our electric rates. A heat pump is rated with a variety of “efficiency ratings” (SEER, HSPF, COP), but the one that is the easiest to look at is COP. This is the “coefficient of performance”, which is an exact efficiency at a given outdoor temperature. When it gets colder outside, a heat pump is a bit less efficient. Even at 32 degrees, a heat pump can often have a COP of 3. This means it is three times as efficient as electric resistance heat (baseboard or electric air handler “furnace”), or uses one third of the electricity. If you apply that to your math, you will see why heat pumps are more efficient that propane.

With our fairly consistent electric rates, it would take propane dropping below $1.00 per gallon to be cheaper than a heat pump.

The second part of your question is around the “back up” heat source – propane vs. electric resistance air handler “furnace”. You need one or the other (or a gas furnace) as the fan the heat pump hooks up to and as the back up heat source for when it drops below roughly freezing. Since you can add a heat pump to either, this is point of personal preference.

Some people live in areas or have had experiences where they can’t get propane consistently and affordably, so they prefer the predictability of all electric. Other people live in areas where there is not good place for a propane tank or they don’t want a tank on their property.

However, in circumstances as you have outlined, a propane furnace as the “back up” may be the best choice. You can much more easily use it with a generator when the power is out, and if you can get affordable propane, it is indeed more efficient than “electric resistance” back up. In a case like yours, it is very likely we would suggest a heat pump with a propane furnace as a very viable solution to consider.

The trick beyond that is choosing which furnace and heat pump – as there are many choices of each and how they match up. For that, we offer free in-home estimates, no obligation, so we can better match them with your specific home and other possible preferences.

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