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Combustion Air Calculator

How much air an appliance needs, from its input rating — for natural gas or propane.

Appliance input (BTU/h) Fuel

How it works

Divide the appliance input by the heat content of the fuel to get the volume of gas burned, then multiply by the air each cubic foot of that gas needs.

Natural gas — about 1,000 Btu/ft³, needing about 10 ft³ of air per ft³ of gas
Propane — about 2,520 Btu/ft³, needing about 25 ft³ of air per ft³ of gas

Propane carries far more heat per cubic foot and needs far more air to burn it. Both halves of that matter, and questions often test whether you have kept them straight.

A note on the exam

G3 questions distinguish between combustion air, excess air and dilution air. This calculator gives air for combustion. Total air requirements in exam questions often include the excess and dilution components as well, so read which one is being asked for.

Studying for the G3 exam?

This is one of the figures the Ontario G3 exam expects you to know without reaching for a calculator. The app has 1,184 practice questions across all 9 syllabus topics, with a free 20-question mock exam.

Try the free mock exam →

Gas properties and conversions →

Gas properties and combustion →

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