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Why Is Furnace Sizing Important?

February 19, 2019

(View as a downloadable PDF version)

Tired of putting up with a cold house or inconsistent heating? It could be that your furnace is improperly sized for your home.

Furnace Sizing & Efficiency Explained


A furnace’s “size” is its capacity to heat a particular space. Furnace sizing is measured in BTUs, or British Thermal Units.


Furnace efficiency is measured in AFUE, or Annual Fuel Utilization Efficiency. The more efficient the furnace, the lower your annual heating costs. The most efficient furnaces have an AFUE rating of 90% or higher.

Signs That Your Furnace Is Improperly Sized


A furnace that is too large will heat your home quickly, but not evenly. It will turn on and off often, reducing efficiency and increasing wear and tear.


A furnace that is too small will run constantly without ever achieving an ideal level of comfort. This also wastes energy and leads to premature failure.

Have an HVAC Expert Size Your Furnace

When installing a new furnace in your home, your HVAC specialist should perform a Manual J calculation to measure your home’s heating load. This takes into account factors like:

  • Square Footage
  • Home Design
  • Windows
  • Air Leakage
  • Insulation

Considering a new furnace for your home?

We offer a wide range of heating services, including furnace replacement. We’ll help you find the right size, most efficient furnace for your home, so you can enjoy greater comfort and lower energy bills.

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