How to Determine BTUs on Gas Powered Equipment
The National Fuel Gas Code mandated by the National Fire Protection Agency provides average BTU consumption rates per hour (BTUH) for gas appliances. According to the Code, clothes dryers average about 35,000, stoves 65,000, ovens 25,000, water heaters 45,000 and tankless water heaters 140,000 to 430,000 BTUH.
Things You Will Need
 Gas meter
 Timer
 Calculator
Of course, results will vary depending on whether appliances are conventional or high efficiency. Your equipment should have nameplates that state the BTU usagefollow the steps below to verify these numbers or to calculate your typical usage rate.

Shut off all gas equipment except for the one you are measuring. Turn on the appliance you are measuring to the setting at which you typically use it.

Watch the gas meter and measure how many seconds it takes to use one cubic foot of gas. Divide 3,600 by the result to obtain cubic feet per hour. For example, 3,600 divided by 140 seconds equals 25.71 cubic feet per hour.

Calculate BTUH for propane by multiplying cubic feet per hour by 2,516. Using the above example: 2,516 multiplied by 25.71 equals 64,700 BTUH (rounded off).

Calculate BTUH if you are using natural gas by multiplying cubic feet per hour by 1,030. For example, 25.71 multiplied by 1,030 equals 26,481 BTUH.

Repeat the steps above for each appliance. Remember to turn any essential appliances back on after you finish testing.