How efficiently a furnace turns fuel into heat, as a percentage.
AFUE is the percentage of fuel a furnace or boiler converts into usable heat over a season. An 80% AFUE furnace delivers 80% of the fuel's energy as heat and loses the rest through exhaust. High-efficiency condensing furnaces reach 90–98.5% AFUE. Higher AFUE means lower fuel bills.
Why AFUE matters
Efficiency terms affect operating cost, rebate eligibility, and how confidently you can compare one quote against another. A higher rating can lower utility bills, but only if the system is sized, matched, and installed correctly.
When you'll see this term
You will usually see this term on equipment proposals, AHRI matches, rebate paperwork, energy labels, and replacement comparisons.
Questions to ask your technician
- How does this rating change my expected operating cost?
- Does this equipment qualify for any current utility or manufacturer rebate?
- Is the indoor and outdoor equipment matched so the rating is valid?
AFUE, SEER2 & HSPF: efficiency ratings explained
Related terms
- SEER2 (Seasonal Energy Efficiency Ratio 2)
- The cooling-efficiency rating for ACs and heat pumps — higher is better.
- HSPF2 (Heating Seasonal Performance Factor 2)
- The heating-efficiency rating for heat pumps — higher is better.
- Furnace
- A heating unit that burns gas or uses electricity to warm air.
- Heat Exchanger
- The furnace part that transfers heat to your air while containing combustion gases.