What Is an AFUE?
Annual Fuel Utilization Efficiency — the percentage of fuel a furnace converts to usable heat. A 95% AFUE furnace turns 95 cents of every fuel dollar into heat; the rest is lost as exhaust.
Why It Matters to You
A higher AFUE furnace wastes less fuel every time it runs, which lowers your heating cost over the winter — the size of the difference depends on your specific usage and current unit's rating.
Practical Guidance
If your furnace is old enough that its AFUE rating isn't on a visible nameplate or is below 80%, ask for its rating during your next service visit so you can weigh replacement against continued repairs with real numbers.
AFUE Efficiency Tiers
| Tier | AFUE Range | Notes |
|---|---|---|
| Standard | 80% | Federal minimum for most new gas furnaces |
| Mid-efficiency | 90-95% | Often uses a sealed combustion/condensing design |
| High-efficiency | 96%+ | Highest tier commonly available; higher upfront cost |
Frequently Asked Questions
What's a good AFUE rating for a furnace?
80% is the federal minimum for most new gas furnaces; 90-95% is considered mid-to-high efficiency, and 96%+ is the highest efficiency tier commonly available.
Why would a furnace not reach 100% AFUE?
Even the most efficient furnaces lose a small percentage of heat through exhaust venting — 100% is a theoretical ceiling, not an achievable rating for combustion equipment.
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