Work out gas cylinder duration instantly with clear inputs, formula shown and shareable results.
LPG holds about 13.8 kWh per kilogram, so a 13 kg cylinder stores roughly 180 kWh. Dividing by the appliance rating gives burn hours: a 7 kW heater consumes about 0.5 kg per hour and empties the cylinder in around 26 hours of continuous use.
Cylinder duration
energy = mass x calorific value; hours = energy / appliance kW; kg per hour = kW / calorific value
Weigh the cylinder and subtract the tare weight stamped on the collar. Warm water down the side also reveals the liquid level by the temperature change.
The gas draw-off rate falls in cold weather because vaporisation slows, so a large appliance may not get full flow even with gas remaining.