By Anne Fonda
A dual fuel heat pump system, also known as a hybrid heating system, pairs an electric heat pump with a gas furnace. “Dual fuel” means that there are two heating sources that alternate between two fuel sources to maximize efficiency and keep you comfortable.
The heat pump acts as an air conditioner in the warmer months and switches to heating mode when the weather cools down. Depending on the heat pump, it can provide 100% of the heat you need until the temperature drops below freezing.
Cold climate heat pumps (CCHPs)can provide 100% of your heat down to 5°F for our low-profile units, and our upcoming standard-size CCHP will be able to heat your home in sub-zero temperatures.
When the temperatures get too cold for the heat pump to work efficiently, the gas furnace kicks in to heat your home. Your HVAC system makes this change automatically. When the temperatures rise, the heat pump takes over heating duties again.
For example, your heat pump might heat your home all day, but when the temperatures drop at night, the gas furnace takes over to keep you warm.
“As a Systems Engineer, my priority is ensuring all components work together for maximum performance and comfort. Dual fuel HVAC systems combine the efficiency of a heat pump with the dependable heating of a furnace, intelligently switching between the two to consistently meet customer needs—even as outdoor conditions change.”
– Kimberly Sexton, Senior Systems Engineer
If you’re new to a heat pump system, you need to be aware of a couple of things and know that they are completely normal.
Any heat pump system has two coils – the indoor coil and the outdoor coil. In the winter, the outdoor coil is usually 10-20°F colder than the ambient air temperature. Because the coil is colder than the surrounding air, condensation forms, just like it does on something you just pulled out of the freezer.
When the outdoor temperature is low enough, the condensation on the coil freezes. This is when the heat pump enters the defrost cycle, or defrost mode. During the defrost cycle, the heat pump’s reversing valve reverses the flow of refrigerant to heat up the outdoor coil, essentially putting the heat pump into cooling mode for a few minutes. After the ice melts, the heat pump reenters an energy-efficient heat mode.
It’s a needed and normal process that may cause a cloud of steam to rise from the outdoor unit. You may also notice cool air coming from your supply registers for a few minutes during the defrost cycle.
When AUX or AUX heat displays on your thermostat, it means your dual-fuel heat pump system has switched to the auxiliary heat source, or furnace heating. The same thing would display if the electric resistance heat strips on a standard heat pump system were activated.
When should aux heat kick in on a dual-fuel system?
Your backup heat source/furnace should come on when your heat pump is struggling to heat your home. The thermostat will trigger Aux heat when:
That last one is because your heat pump system can take a while to increase the temperature in your home. If you suddenly raise the temperature by more than 2 degrees, the thermostat will trigger aux heat to help reach the new set temperature faster.
It’s important to note that your furnace will not kick in during the heat pump defrost cycle. That’s because the heat pump and furnace cannot operate simultaneously.
Because a dual-fuel heating system automatically chooses the most efficient way to heat your home, you can save energy and money. Your actual savings will depend on the electricity rates and natural gas rates in your area.
Some utility companies offer a winter discount for electricity rates if you own a heat pump, so be sure to sign up for that rate if it’s available. They charge a lower kilowatt per hour (kWh) rate from November to April.
The backup electric heat strips sold with many new heat pump systems can jack up your electricity usage in cold weather, which means high energy bills. Using a gas furnace as your backup heating system can be much more cost-effective.
A dual fuel heating system can not only save you money in the long run, but the system upgrade may qualify for a heat pump rebate. Check with your local utility company and HVAC installer about available incentives in your area.
Anne Fonda, Content Writer
A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.
She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.
Expert review by Kimberly Sexton, Senior Systems Engineer
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