What’s the Right-Sized Furnace? (and Why it Matters!)

December 1, 2021

smarthouse furnace sizing infographic

(View as a downloadable PDF version)

Size matters—especially when it comes to furnaces! If you’re suffering from a cold house and inconsistent heating, the problem could be your furnace sizing.

Too Large

A furnace that’s oversized may heat your home up quickly, but unevenly. It will start and stop too often, cutting your energy efficiency and adding wear and tear.

Too Small

An undersized furnace will run constantly but never achieve desired even heating. With no downtime, furnaces that are too small waste energy and can fail prematurely.

By the Numbers: Your Furnace Rating


BTU, or British Thermal Unit, indicates the capacity or power of a furnace system to heat the necessary space.


AFUE, or Annual Fuel Utilization Efficiency, refers to how efficiently the unit turns fuel into heat. Energy efficient new furnaces have an AFUE rating of around 90% to save energy and dollars.

Have an HVAC Expert Choose the Right Sized Furnace for You

Following industry-standard Manual J calculations, the HVAC experts from SmartHouse Heating and Cooling will consider a number of different factors that affect gas furnace sizing, including: 


Thinking about upgrading your furnace?

The heating experts at SmartHouse Heating and Cooling will calculate a new furnace that is just the right size to heat your St. Louis area home both efficiently and effectively. Your neighbors have relied on SmartHouse for heating services, including furnace replacement, heating maintenance and repair.

Make sure your furnace is sized right! Call 314-644-1570 or contact SmartHouse today for expert HVAC installation.