Understanding furnace energy ratings

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Furnace RatingsWhen it comes to replacing your home furnace you’ll be considering a lot of options, including energy efficiency. AFUE ratings (Annual Fuel Utilization Efficiency) determine how well a specific furnace uses energy. It’s similar to the miles-per-gallon rating on a new car.

The Department of Energy defines AFUE as the ratio of annual heat output compared to the total annual fossil fuel energy used by the furnace. An AFUE of 80% indicates that 80% of the energy in the fuel transfers into heat, while difference, 20%, is lost. It’s measured at the output vent of the furnace and does not include heat loss via the ducts. Here’s what the energy guide label looks like.

Energy Guide Example

If your older furnace doesn’t have a label, you can estimate what the efficiency is. Furnace that have pilot lights that are on continuously are most likely low efficiency. These systems are typically between 56-70% efficient. High efficiency furnaces use two heat exchangers and are typically 96-98% efficient

Here are the minimum efficiency standards as outlined by the Department of energy:
Furnace Type

  • Gas 80% efficient
  • Mobile home 80%
  • Oil 83% efficient
  • Most gas furnaces in the northern states are required to be 90% efficient.

Lower your energy bills

If your energy bills are rising or if repair costs are becoming a problem, consider replacing your furnace. Installing a new high efficiency model will save you a bundle each month plus many local energy companies provide incentives and rebates when you put in a new furnace.

In your quest to buy a new furnace, check out our blog, That big box in the basement, to learn what you need to know about the types and sizes of furnaces.


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