Glossary · Heating, cooling & ventilation
Dual-fuel (hybrid) system
Also called: dual-fuel heat pump · hybrid heating · hybrid heat pump · hybrid system · heat pump with gas backup · dual energy
A heat pump paired with a gas, propane or oil furnace or boiler; controls switch to the fuel when it's colder or cheaper to do so.
What it means
The heat pump handles most of the year and the furnace takes over below a set outdoor temperature, usually the economic balance point. The two don't run at the same time. It can make sense where winters are very cold, gas is relatively cheap or the existing furnace is fairly new.
Why it matters in an audit
It can cut fuel use and emissions while keeping a fuel backup, but rebate eligibility for hybrid setups varies by program.
In the United States
DOE's May 2026 HEEHR changes let households keep an existing fossil-fuel system when they add a heat pump.