Glossary · Heating, cooling & ventilation
AFUE (annual fuel utilization efficiency)
Also called: furnace efficiency · boiler efficiency · AFUE rating
The share of a furnace's or boiler's fuel that ends up as heat in your home over a year; a 95% furnace loses about 5% up the vent.
What it means
AFUE counts losses up the chimney or vent but not heat lost from leaky or uninsulated ducts, which can be large. Mid-efficiency furnaces are about 80%, and condensing furnaces reach 90% or more; older furnaces with standing pilot lights score lower.
Why it matters in an audit
Knowing your furnace's AFUE lets the auditor estimate what a replacement or a heat pump would save, and AFUE minimums decide what can legally be installed.
Typical numbers
Reference values with their sources. Your energy advisor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| Canada minimum, gas furnaces up to 65.92 kW (225,000 BTU/h), made on or after July 3, 2019 | 95% (80% allowed for replacement non-condensing and relocatable-building furnaces) | laws-lois.justice.gc.ca ↗ |
In Canada
Canada has required condensing-level efficiency (95% AFUE) for most new gas furnaces since July 3, 2019, with narrow exceptions.