How to gas rate an appliance
- Turn off all other gas appliances in the property.
- Run the appliance at its maximum rate and let it settle.
- Enter the initial meter reading and start the timed test. 2 minutes is standard.
- When the countdown reaches 0:00, read the meter and enter the final reading.
- Compare the result with the appliance data plate and the manufacturer's instructions.
The formula
Gas rate (m³/h) = (final − initial) × 60 ÷ test minutes
Gross heat input (kW) = m³/h × CV × 1.02264 ÷ 3.6
Net heat input (kW) = gross ÷ net factor
Natural gas uses a CV of 39.5 MJ/m³ and a net factor of 1.1. LPG (propane) uses 93.1 MJ/m³ and 1.085. Imperial readings are converted at 1 ft³ = 0.0283168 m³. 1.02264 is the volume correction factor used on UK gas bills, and dividing by 3.6 converts MJ per hour to kW.
This calculator is a tool to help with the arithmetic. Always follow the manufacturer's instructions and current industry guidance when commissioning or servicing an appliance.