AFUE (Annual Fuel Utilization Efficiency) is the efficiency rating for gas, propane, and oil furnaces. It expresses what percentage of fuel energy is converted to useful heat over a full heating season.
The federal minimum for natural gas furnaces is currently 80% AFUE. "High-efficiency" condensing furnaces reach 90-98% AFUE by capturing heat from flue gases that would otherwise be vented — they look different from standard furnaces (PVC flue pipes instead of metal, and they produce condensate that must be drained).
For SC, a mid-tier 90-92% AFUE furnace is often the right balance of efficiency and equipment cost. 95%+ AFUE pays back faster in colder climates than ours.
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