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...all in one package. It essentially combines an air cleaner, humidifier, dehumidifier, ventilator, heat pump, and gas furnace one box. Additionally the control system that comes with these units often allows for multiple control zones. This improves flexibility of thermal comfort when mom and dad are cold but the kids are warm!
A nice side feature of these packaged systems often include humidity control.
Humidity problems can be a very underrated issue that cause many issues within a home. Humidity levels can encourage or discourage growth of mold, viruses, and bacteria; as well as significantly improve thermal comfort. Humidity control in your HVAC system is a huge plus!
The best way to discuss these heat pumps is by looking at a few examples.
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 of its features include:
This is Carrier's top of the line packaged heat pump. And additional bonus is the sound ratings for this unit. It is quieter than a standard outdoor condensing unit due to the additional sound insulation and unit casing materials. A few additional bells and whistles...detects when your air filter needs to be changed and controls humidity in your home.
See Carrier's consumer brochure for their dual fuel heat pump.
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.