Most dual-fuel heat pumps have a heat pump for heating and cooling a structure in temperate weather and gas or oil furnace components for especially cold times. Systems can typically be set to switch automatically when the temperature changes.
While in heating mode, heat pumps transfer warmth in the air or ground outdoors inside the structure. When the temperature is fairly mild, this process is more efficient than running a furnace or boiler would be. If there is little warmth to extract, however, the heat pump uses far more electricity and may not be able to keep up.
By burning gas or heating oil when the temperature drops below a particular level, homeowners using dual-fuel heat pumps can spend less on their heating bills. Having two separate heating systems provides redundancy as well; if one heating component fails, the other can generally still run. People living in remote areas may want to consider a dual-fuel heat pump to ensure access to heating.
Almost all heat pumps have an emergency heating mode that activates when the unit cannot generate sufficient heat. This mode typically uses electrical resistance to generate heat and functions much like older electrical heaters. Running in emergency heating mode is expensive, however, so a dual-fuel heat pump may be a wise investment for homeowners who regularly rely on emergency heating mode.