Dual-fuel systems can protect homeowners from rising utility costs. They're more energy efficient, provide greater comfort, and have a smaller carbon footprint.
A hybrid heating system is the combination of an air source heat pump (ASHP) or ground source heat pump (GSHP) with a propane or natural gas furnace. Hybrid heating systems, which may also be called dual-fuel systems, improve ASHP and GSHP performance by using a propane furnace — typically a high-efficiency unit — in colder, outdoor temperatures, rather than the heat pump's inefficient electric resistance secondary heat. By relying on the high-efficiency propane furnace during colder periods, the overall heating system is more energy efficient, provides greater comfort, and has a smaller carbon footprint.
Hybrid heating systems are a good alternative to ASHP-only or GSHP-only systems, especially in mixed and colder climates where winter temperatures will fall below approximately 40 degrees Fahrenheit. At these lower outdoor temperatures, ASHPs will rely more on electric resistance back-up heat. By using the high-efficiency propane furnace to heat the home during colder outdoor temperatures, the hybrid system maintains efficiency, delivers warm air, and reduces electricity costs, which rise sharply with the use of electric resistance back-up.
Hybrid heating systems offer the ability to use both a high-efficiency heat pump (which offers heating and cooling benefits) and a high-efficiency furnace to efficiently and comfortably address colder winter conditions. In the case of ASHP-furnace hybrids, when the propane furnace cycles on for heating — typically at a transition point near 40 degrees Fahrenheit — it greatly boosts the heating system's output capacity and also ensures that warm air delivery temperatures of around 120 degrees Fahrenheit leave the furnace.
Hybrid heating systems also provide a homeowner with an energy choice. As energy prices fluctuate, or if the homeowner prefers the warmer air delivery of the furnace, the transition point can be adjusted upward or downward. Hybrid systems also provide a redundant heating system. If the ASHP compressor experiences a problem, the home can still be heated with the high-efficiency propane furnace.
Energy consumption and costs
Hybrids composed of an ASHP and a high-efficiency propane furnace save nearly $400 per year compared with a standard efficiency ASHP-only system (see table below). In existing homes with an older ASHP, at the time of system replacement (about 10–15 years) the marginal first cost for upgrading to a hybrid system instead of another ASHP-only system is about 14 percent. The hybrid system offers a 2.5-year payback, based on its annual energy savings. Also, government and industry incentives worth hundreds or thousands of dollars are available for hybrid systems.
Cold Climate Annual Heating & Cooling Costs for a 2,400-square-foot Home
|HVAC SYSTEM||ANNUAL ENERGY COST|
|Hybrid HP: High-efficiency ASHP & high-efficiency propane furnace||$1,715|
|Standard-efficiency ASHP with electric resistance back-up||$2,103|
See the full analysis of the results, including cost comparisons of heating and cooling systems in larger homes, in our hybrid heating systems fact sheet (pdf).