What are furnace Ratings?

Furnace ratings tell you how much fuel actually becomes usable heat

The main furnace rating you'll see is AFUE, or Annual Fuel Utilization Efficiency, expressed as a percentage. A furnace rated 90% AFUE converts 90% of the fuel it burns into heat for your home, with the remaining 10% lost as exhaust through the flue. The higher the number, the more efficient the furnace.

What counts as a good AFUE rating

• 80-83% AFUE: standard-efficiency, common baseline for gas furnaces
• 90-95% AFUE: high-efficiency, condensing furnaces that reclaim more heat from exhaust gases
• 96%+ AFUE: top-tier efficiency, typically the highest upfront cost

A higher AFUE furnace generally costs more to buy but less to run, so the right rating for your home depends on how long you plan to stay in it and your local utility rates.

AFUE isn't the whole picture

AFUE only measures fuel-to-heat conversion — it doesn't account for duct leaks, poor insulation, or an incorrectly sized system, all of which can waste the efficiency a high-AFUE furnace is supposed to deliver. A 95% AFUE furnace connected to leaky, uninsulated ductwork can perform worse in practice than an 85% AFUE furnace on a tight, well-sealed system.

Other ratings worth knowing

For cooling equipment and heat pumps, you'll also see SEER (Seasonal Energy Efficiency Ratio) and HSPF (Heating Seasonal Performance Factor) — related but separate measures that apply to the compressor side of a system rather than a gas furnace's combustion efficiency.

Why the rating on the box isn't the whole decision

Two furnaces with the same AFUE rating can still perform differently depending on build quality, blower type, and how well they're matched to your home. Use AFUE as one input alongside a proper load calculation, not as the single deciding factor.

Not sure which AFUE rating makes sense for your budget and home? Call LJ Refrigeration Co. at (480) 948-5004 and we'll help you compare real numbers, not just the label.