A dual fuel, or hybrid, system runs a heat pump most of the year and switches to a gas furnace in deep cold. It is designed to hand each fuel the job it does most cheaply, which makes the switchover setting the heart of the system.
What it is and how it switches
Trane defines a dual fuel HVAC system as a hybrid system made up of both an electric heat pump and a gas furnace. The two do not run at once. Trane explains the system operates on electricity, the heat pump, most of the time and switches to the gas furnace whenever temperatures get cold enough that it is needed. This lets the efficient heat pump carry mild and moderate weather while the furnace steps in for the coldest stretches, rather than forcing one appliance to cover the whole range.
The economic balance point
The switchover is not arbitrary; it is tied to cost. The Minnesota ASHP Collaborative reports that the economic balance point for homes to switch from a heat pump to a natural gas furnace is between 25F and 45F. The Collaborative describes the switchover temperature as the point where switching to the furnace when outdoor temperatures are too cold lets homeowners minimize energy bills while electrifying part of their heating. Above that point the heat pump is cheaper heat; below it, gas may be, depending on local prices.
How the switchover setting changes your bills
Where you set the switchover directly controls how electric your heating is. The Minnesota ASHP Collaborative reports that setting the switchover to 45F uses the heat pump for roughly 30% of the heating hours in a typical year, while a 25F switchover uses it for roughly 56%. A lower switchover means more heat-pump run time and more electrification; a higher switchover leans on the gas furnace. That one dial is how a dual fuel owner balances operating cost against carbon and comfort. ENERGY STAR adds context that a cold climate heat pump will continue working below 5F, but pairing it with a backup energy source heats most efficiently when temperatures are even lower.
Equipment cost, best fit, and the emissions caveat
Dual fuel can also lower the heat pump's own price. Slipstream notes a dual fuel heat pump can be sized smaller and does not need the same cold-temperature capacity retention required if it were shouldering the entire heating demand. Alternative Aire frames the ideal case as colder climates with cheap natural gas, where a dual fuel system lets the heat pump handle milder months and the furnace provide cost-effective heat below freezing. There is an honest caveat: Slipstream notes that where electricity comes mainly from fossil fuels, powering a heat pump on the coldest days might be dirtier than burning fuel onsite in a dual fuel system. The right switchover balances cost, comfort, and local grid emissions.
Frequently asked questions
What is a dual fuel system?
Trane defines it as a hybrid system made up of both an electric heat pump and a gas furnace, running on the heat pump most of the time and switching to gas when it gets cold enough.
At what temperature does it switch to gas?
The Minnesota ASHP Collaborative reports the economic balance point is between 25F and 45F, the range where switching fuels minimizes bills.
How much does the switchover setting matter?
A lot. The Collaborative reports a 45F switchover uses the heat pump about 30% of heating hours, while a 25F switchover uses it about 56%.
Is dual fuel cheaper equipment?
It can be. Slipstream notes the heat pump can be sized smaller and does not need full cold-temperature capacity retention, since the furnace handles the coldest days.
Is dual fuel always greener?
Not necessarily. Slipstream notes that where electricity is mainly from fossil fuels, running the heat pump on the coldest days might be dirtier than burning fuel onsite.