Unless you live very far north (Maine, Minnesota, etc), the benefits of dual fuel vs just a heat pump are becoming diminishingly small. Especially with propane ($$) as your auxiliary fuel.

Edit: this is from a cost-to-operate perspective. If you need resiliency (do you often suffer from power outages?), dual fuel with propane may make sense. You will still however need some renewable electric supply to run the air handler.

One factor that can be a problem is recovery from a setback. Many prefer a lower indoor temperature for sleeping. Imagine an overnight setback temperature of, say, 5-10 degrees lower and then having only a heat pump to raise the interior temp from the setback at 6am when the overnight temperature is at its lowest and a heat pump's ability to produce heat is accordingly also at its lowest. A propane furnace supplement produces more heat at lower cost than electrical resistance strips often used for "emergency" or recovery heat with heat pumps.

I had a dual-fuel heating system in my previous home (I live in coastal Virginia.) The advantage is that use of the more expensive fuel (natural gas in my case) is avoided during those periods when the heat pump can provide adequate heat. It's also a great back-up heating system in the event of a power outage as noted by another poster above. My 6 kW generator could easily power the gas-fired furnace and plenty of other stuff, too. It wouldn't be able to start the heat pump.

A dual fuel system allows you to choose which fuel will provide the lowest heating cost. In most parts of the US heating with a heat pump will cost less than propane. If you post your electric rate and propane costs a rough calculation can be done of the cost savings.

Another benefit is if you run out of propane, you can use the heat pump as the back up heating system. If there is a power black out, it would be possible to run the propane furnace using a portable generator.

Its difficult to justify the added cost of a furnace system in a dual fuel setup except in a very small number of localities. It's basically two systems with almost double the up front cost and rarely breaks even compared to the added cost of electric backup. If you live in an area where the weather is so cold that backup heat is used most of the time, just get a (natural/propane) gas furnace. Otherwise, just get a heatpump with electric backup.

You'll definitely want to run the numbers before deciding. To be sure, propane is more expensive than natural gas.

Not if it costs $10,000 to connect to Natural Gas. (My situation.)

A dual fuel system does not have to be two systems at about twice the cost.

"A dual fuel system does not have to be two systems at about twice the cost."

Well, maybe not exactly twice the cost but but not sure how a dual fuel system doesn't involve two systems (heat sources).

HVAC contractors positively salivate when the hear "dual fuel"!

" If you install a dual fuel split system, then the furnace acts as the air handler in the same manner it does for an AC only split system. The extra cost is the outdoor heat pump condenser and upgraded thermostat. "

I think you know how it works but what you said isn't exactly correct. The furnace provides the blower function but not a heat exchanger. A separate evaporator coil is needed both for straight AC and heat pump operations. In a straight heat pump install without a dual fuel capability, the evaporator coil and the blower are in the air handler.

With dual fuel, the incremental initial cost is the cost of the gas burner, associated controls and gas piping versus the cost of the electric strip heaters, wiring, and any required circuit controls and disconnects. It's not a trivial cost, so it's good to run the numbers before deciding. Some of my clients prefer the "comfort" of gas heat during a cold snap. For them any economic analysis is moot.

@Elmer J Fudd

You are correct. The furnace provides the only blower function. A coil is required if either for an AC or heat pump condenser.

@Charles Ross Homes

What you say is true for a new build where nothing exists. I always think in terms of equipment replacement where a gas piping and electrical wiring are in place and can be reused.

The original question was about the benefit of a dual fuel system using propane and a heat pump. The original author will need to provide details of what exists today in order to have a meaningful discussion of the incremental cost compared to a single fuel system.

In the case of a dual fuel system as a replacement for a furnace and air conditioner, the incremental cost would be lowered by the existing availability of gas piping. If it's being considered as a replacement for a heat pump with strip heaters, the cost to run gas piping would need to be considered. Some propane companies in our area will run the gas piping at little to no cost for a customer with a large tank and long-term contract.

@mike_home The original question was about the benefit of a dual fuel system using propane and a heat pump. The original author will need to provide details of what exists today in order to have a meaningful discussion of the incremental cost compared to a single fuel system.

We currently have an oil-fired hot air system which we plan to replace as part of a renovation project. So the electric and propane infrastructure would have to be created from scratch in order to support a dual fuel system.

Another option is to create a dual fuel system using fuel oil. This would allow you to reuse your existing fuel oil tank. That may not be appealing if you are looking to get rid of an indoor tank.

@mike_home Another option is to create a dual fuel system using fuel oil. This would allow you to reuse your existing fuel oil tank. That may not be appealing if you are looking to get rid of an indoor tank.

No, we definitely want to get rid of the oil tank. Thanks so much for weighing in.

So how much do you figure it will cost to get rid of your oil tank? lol

My cost of fuel per year is peanuts here in Maryland because the Heat Pump is used usually to heat - except in extremely low temperatures.

What is your location? Propane is very expensive depending whether you or the propane company owns the tank. You might be better off using electric heat strips as the back heating and forego the dual fuel system. Investigate what other houses in your neighborhood have done when they eliminated their fuel oil system.