The dual fuel heat pump (also known as a hybrid heat pump) is a great concept that offers real performance in all weather conditions.
The big knock against heat pumps....
Air source heat pumps cannot operate under approximately 40 F...and in the 40-50F range it is not very efficient when operating as a heater.
The dual fuel is simply a standard air source heat pump with a gas furnace add-on.
The control system on these heat pumps use the gas furnace at just the right temperature.
The best way to discuss these heat pumps is by looking at an example.
The heat pump above is Trane's XL16c Earthwise Hybrid heat pump. It offers:
The Trane unit that you see above is a packaged, all-in-one system. So the ducting from your house or building would be connected to the heat pump. The fan, furnace, heat pump, etc. are all housed in this one package. It can be installed outside your building at grade or on the roof.
The Carrier Infinity Hybrid Heat Dual Fuel System is Carrier's packaged offering. It is Carrier's competitive offering to the Trane XL16c Earthwise Hybrid. Some its features include:
This is Carrier's top of the line packaged heat pump.
However if you would like better efficiency, Carrier developed a dual fuel heat pump control system. This allows one to use Carrier's Infinity 96 gas furnace and Carrier's Infinity 19 heat pump conjunction with each other.
It accomplishes the same purpose of a packaged system with the following differences:
In general the dual fuel heat pump is a great solution for regions that have large swings in weather. If your winter gets very cold (near and below freezing) and your summer requires air conditioning, this is a very good option for you.
If you are installing or replace both a heating and cooling system, don't make a decision without considering this type of heat pump system.