Question Regarding Dual Fuel Heating: Heat Pump and Propane Furnace

[blues]

We're in Ohio. We have Geo Thermal plus propane. Our propane comes on at around 20*. It was set that way when it was installed, I think. There is a sensor outside that reads the outside temp. Our thermostat automatically switches from AC to heat when needed. We set it to cool to 75* and heat to 69* and leave it there year round.

Close to what we do. 75 and 67

[0ddl0t]

So, clearly they will work down pretty low...but I wonder how the cost vs. the $3 / gallon for the propane furnace works out from an efficiency standpoint once the temp drops into single digits. (I'm way too lazy and ignorant to try to plot that chart.)

1 gallon of propane has 27-28 kWh of energy, so at $3/gallon your propane costs about $0.11 per kWh

At 10°F, your heat pump is 2.7x more efficient than propane, so electricity needs to cost you over $0.30 per kWh for propane to be cheaper.

[TDA]

Where you live is definitely a factor, less so for propane prices than your electric rates, and even more so for geothermal where your geology will dictate drilling costs unless you’re doing a lake loop or something else weird. Good ductless mini splits work really well down into single digit outdoor temps, but efficient isn’t resilient and I wouldn’t go pulling out a heating oil or propane system that I could just leave turned off while electricity was cheaper. If your utility is going to give you free money to install ductless splits though, that’s an important consideration and I’d do it, particularly if I didn’t have central AC and I was getting DHPs that cooled as well. They beat window or sleeve type AC units like a gong.

[HeavyDuty]

This house is my first experience with a heat pump. We were down in the low teens the last few weeks, and it had no problem keeping up in normal mode and maintaining a 72 degree interior. We are also very, very well insulated which I’m sure helped.

I’m glad, because our emergency heat is electric…

[blues]

This house is my first experience with a heat pump. We were down in the low teens the last few weeks, and it had no problem keeping up in normal mode and maintaining a 72 degree interior. We are also very, very well insulated which I’m sure helped.

I’m glad, because our emergency heat is electric…

My heat pump is good down to about 9 or 10 degrees, after which it starts to lag and my furnace will be called up (as auxiliary heat). Then it switches back to the pump without me ever having to do anything.

[HeavyDuty]

My heat pump is good down to about 9 or 10 degrees, after which it starts to lag and my furnace will be called up (as auxiliary heat). Then it switches back to the pump without me ever having to do anything.

Huh. Now I wonder if mine actually switched to emergency heat all by its lonesome.

[blues]

Huh. Now I wonder if mine actually switched to emergency heat all by its lonesome.

Depends on where they set the crossover point. I know they set mine low.

The other thing is that if the pump struggles and the indoor temp drops a couple / three degrees below where you set the thermostat, it will automatically switch even if above the crossover point temp setting.

[UNK]

I think mine is set above freezing by a few degrees. Mines only a few years old, at the recommendation of my contractor I didnt spring for a high end unit.

[mmc45414]

I am jealous, I do not have a good place to park the tank, so no propane (insert sad trombone...).

But I wonder about rather than precisely calculating the cost break point, I might switch when the heat pump is working hard. It might cost a little less, but that is a complex system with expensive compressors grinding away just to do what a simple flame that isn't going to wear out (the blower has to run either way) could be doing instead. Maybe spending an extra couple hundred a year might make the heat pump last a few years longer?

We just got done with it being in the teens for about ten days, and at the beginning of the cold stretch I turned it down at night (we like it cooler while we sleep) and that was a dumb decision, it ran a few days to get back, including diligently using the fireplace stove to augment it.

[UNK]

I am jealous, I do not have a good place to park the tank, so no propane (insert sad trombone...).

But I wonder about rather than precisely calculating the cost break point, I might switch when the heat pump is working hard. It might cost a little less, but that is a complex system with expensive compressors grinding away just to do what a simple flame that isn't going to wear out (the blower has to run either way) could be doing instead. Maybe spending an extra couple hundred a year might make the heat pump last a few years longer?

We just got done with it being in the teens for about ten days, and at the beginning of the cold stretch I turned it down at night (we like it cooler while we sleep) and that was a dumb decision, it ran a few days to get back, including diligently using the fireplace stove to augment it.

What really prolongs the life is cleaning the coils bi yearly. At least thats what I was told.