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Accurately determining the heat output of a fuel is essential when sizing heating equipment for any building. For gas fuels like propane and natural gas, the heat produced is directly tied to the volume of gas consumed, measured in cubic feet per hour (cfh). Converting that consumption rate into British Thermal Units (BTUs) allows engineers to choose the proper furnace size and ensure efficient, reliable heating.

Step 1 – Measure Hourly Gas Usage

Start by recording the total gas volume used over a 24‑hour period via your gas meter. Divide that figure by 24 to find the average hourly consumption in cubic feet. This average cfh is the foundation for all subsequent calculations.

Step 2 – Identify the Fuel’s Heat Value

Each fuel type has a standard heat content per cubic foot. For the most common fuels:

• Propane: 2,500 BTU per cubic foot
• Natural gas: 1,050 BTU per cubic foot

Write down the appropriate value for the fuel you are evaluating.

Step 3 – Convert to BTUs per Hour

Multiply the average hourly consumption (cfh) by the fuel’s heat value (BTU per cubic foot). For example, if a system consumes 15 cfh of propane, the hourly heat output is:

(2,500 BTU / cfh) × 15 cfh = 37,500 BTU / hour.

Use this figure to match your heating equipment’s rated capacity and to optimize system performance.