What is a dual fuel heat pump, and does a Florida home need one?

What a dual fuel system is

Carrier, a maker of heating and cooling equipment, describes a dual fuel heating system as one that combines an electric heat pump with a gas furnace. Goodman, another maker, says it may come as a packaged unit or a split system. For the difference, see our guide to package units and split systems.

ENERGY STAR, the federal efficiency label program, says dual fuel systems allow heating with a heat pump or with a more traditional gas or oil furnace. It says this lets you use each system optimally based on costs and environmental benefits.

When the system calls for cooling, Goodman says the heat pump works just like a central air conditioner.

The heat pump itself runs on electricity.

How the system decides which part runs

The Building Science Education Solution Center, a Department of Energy (DOE) training site, says heat pumps lose efficiency and capacity at lower outdoor temperatures and higher heating loads.

The DOE training notes name two main control methods. The first is the balance point method. The balance point is the outdoor temperature where the heat pump can no longer provide enough heat to maintain comfort. Below it, the controls switch to the backup system, so only one system is on at a time.

The same notes say the balance point is programmed in the controls for automatic changeover at 5°F to 35°F, depending on system capabilities. They say it is found from load calculations and the heat pump's performance data.

The second is the droop method, also called simultaneous operation. Here the backup system's setpoint, its target temperature, is set 3°F colder than the heat pump's. When the heat pump alone cannot keep up, the backup runs along with it.

Carrier adds that there is not one universal temperature at which every dual fuel system switches to the furnace. It says the balance point can vary based on the equipment, home, climate and energy costs.

Why some homes choose dual fuel

Carrier says dual fuel heat pumps can be a useful option in regions with moderate to cold climates. ENERGY STAR says that if you have a relatively new furnace with an older central air conditioner, a certified heat pump creates a dual fuel system.

ENERGY STAR says a cold climate heat pump keeps working below 5°F, but pairing it with a back-up energy source will heat a home most efficiently when temperatures are even lower.

Carrier says actual operating-cost savings depend on factors such as electricity and natural gas prices, equipment efficiency, climate, system sizing and how the system is controlled.

Carrier names the main drawback as upfront cost and installation complexity. A home has to install and maintain both a heat pump and a gas furnace.

How rarely a Florida home needs one

The Energy Information Administration (EIA) 2020 Residential Energy Consumption Survey (RECS) counted about 8.06 million Florida housing units (homes). It found 5.35 million used electricity as the main heating fuel. Only 0.42 million used natural gas.

The EIA's 2009 Florida summary said Florida residents use space heating equipment much less than those in other states. Neither EIA source counts dual fuel systems, so neither says how many Florida homes have one.

The Florida Solar Energy Center (FSEC), part of the University of Central Florida, says most heating and cooling energy in Florida goes to cooling. FSEC discusses a straight air conditioner with electric resistance heating. It says South Florida's heating season is so limited that this setup makes little difference to yearly HVAC (heating, ventilation and air conditioning) energy use. It adds that this setup is much less efficient than a heat pump.

FSEC's advice for Central and North Florida is to select a heat pump. It does not mention dual fuel at all. Neither did any Florida source we read. For the wider picture, see our guide to central heating in Florida.

The backup a gas furnace replaces

Goodman names the backup a gas furnace would replace: the heat pump's electric heat strip, used when temperatures drop.

Goodman says that where natural gas is an option, homeowners may be able to add a gas furnace, which would be the secondary heat source instead of the heat strip.

ENERGY STAR says a heat pump is more energy-efficient than a furnace or boiler, even during winter. It says that if you have both, you should use your heat pump year-round.

To learn how a heat pump's electric backup works, see our guide to heat pump backup heat. For Florida-specific heat pump concerns, see heat pumps in Florida.

If you are weighing it anyway

The EIA count of 0.42 million shows some Florida homes do heat mainly with gas. Goodman says a licensed dealer may be able to pair a new heat pump with an existing furnace. Carrier says an HVAC professional will need to evaluate the furnace's blower motor. It also names the ductwork and smart thermostat compatibility.

ENERGY STAR says a good contractor will work with you on size and integration with a back-up heating system. It also says the contractor should verify the size with Manual J, a calculation of how much heating and cooling a home needs.

Useful questions to ask are simple. Does the home have gas service now? What balance point would the installer set, and why? How would the controls switch between the two systems?

For a broader comparison, see heat pump versus furnace.