Heat Pump vs Furnace Efficiency
Compare heat pump efficiency (HSPF) with furnace efficiency (AFUE) to find the most cost-effective way to heat your home.
In this guide
- How furnaces generate heat
- How heat pumps move heat
- Understand AFUE and HSPF ratings
- Calculate heating operating costs
- Evaluate cold climate performance
Furnaces generate heat by burning fuel, reaching a maximum theoretical efficiency of slightly under 100%. Heat pumps do not generate heat; they use electricity to move existing heat from the outside air into your home, allowing them to reach efficiencies of 300% or more.
How furnaces work (AFUE)
A furnace creates heat by combusting a fuel, usually natural gas, propane, or heating oil. The efficiency of a furnace is measured by its AFUE (Annual Fuel Utilization Efficiency) rating. This is a simple percentage.
An older furnace might have an AFUE of 80%, meaning 80% of the fuel is turned into usable heat for your home, while 20% is lost as exhaust gases out the chimney. The absolute maximum efficiency a furnace can theoretically achieve is roughly 98%. It is physically impossible for a combustion furnace to exceed 100% efficiency because it cannot output more heat energy than was contained in the fuel it burned.
How heat pumps work (HSPF)
Heat pumps use electricity to run a compressor and circulate refrigerant. Instead of burning fuel to create heat, they act like an air conditioner in reverse—absorbing trace amounts of heat from the cold outdoor air and compressing it to make it hot enough to warm your home.
Because moving heat takes significantly less energy than generating it, heat pumps operate at extraordinary efficiencies, often delivering 3 units of heat energy for every 1 unit of electrical energy consumed. This is known as a Coefficient of Performance (COP) of 3.0, or 300% efficiency.
Why heat pumps exceed 100% efficiency
It sounds like magic, but it's just thermodynamics. By utilizing the free heat stored in the outdoor air (which was put there by the sun), a heat pump only pays the "delivery fee" (the electricity required to run the compressor) rather than paying for the heat itself.
Definitions
- Heating Load: The total heat your home needs, measured in BTUs.
- Efficiency: AFUE for furnaces, COP or HSPF for heat pumps.
Example
Even though electricity costs more per unit than natural gas, a heat pump's 300% efficiency often makes it cheaper to run than a 90% efficient gas furnace.
Worked cost comparison
Let's compare delivering 1 million BTUs of heat using a 90% efficient natural gas furnace versus a heat pump with a COP of 3.0. Assume natural gas costs $1.50 per therm (1 therm = 100,000 BTUs) and electricity costs $0.14 per kWh (1 kWh = 3,412 BTUs).
| Metric | Gas Furnace (90%) | Heat Pump (3.0 COP) |
|---|---|---|
| Input Energy Required | 1,111,111 BTUs | 333,333 BTUs |
| Billed Units | 11.1 Therms | 97.7 kWh |
| Total Cost | $16.65 | $13.68 |
Cold climate considerations
As the outdoor temperature drops, there is less heat available in the air for the heat pump to extract. Below freezing, a heat pump has to work much harder, and its COP drops from 3.0 down to perhaps 1.5 or 2.0. In extreme cold (below -10°F), some older heat pumps must rely on expensive electric resistance backup heating.
However, modern "Cold Climate" heat pumps are specifically engineered with advanced variable-speed compressors that maintain high efficiencies even at sub-zero temperatures.
Limitations
For more information on our calculations, please read our Methodology and Disclaimer.