How it's calculated
Fuel (L/h) = Heat output (kW) ÷ (9.95 kWh/L × 85% efficiency)
Diesel holds about 9.95 kWh of energy per litre, and a diesel air heater turns around 85% of that into heat. This matches manufacturers' figures: a 2 kW heater uses roughly 0.1 L/h on low and 0.24 L/h on full power.
Battery use includes the running draw plus two start-ups a day (about 100 W for 5 minutes each, when the glow plug is on).
Worked example
A 2 kW heater averaging 50% output for 8 hours a night uses about 0.95 L of diesel a night, so a 10 L tank lasts over 10 nights. It takes around 15 Ah from a 12 V battery.
Tips
- Running a heater on low for long periods can coke it up. Run it on high for 20–30 minutes now and then.
- Insulating your van well cuts fuel use far more than any heater setting. See the heat loss calculator.
- Fit a carbon monoxide alarm, and keep the exhaust and intake well apart.
- At high altitude, heaters need an altitude kit or setting to run cleanly.
Frequently asked questions
How much diesel does a 2kW diesel heater use overnight?
Typically 0.8–1.9 L over an 8-hour night, depending on how cold it is and how well insulated the space is.
How much battery does a diesel heater use?
Usually 10–40 W while running, so around 10–25 Ah over a night at 12 V, plus a short spike at start-up.