On startup, diesel air heaters typically draw 6–10 amps for about 2–3 minutes, depending on the model. This initial power use by the glow plug is to ignite the diesel. Once the flame is established, the glow plug turns off, and the heater only uses power to run the fan and onboard computer.
Ongoing power consumption is very low—typically 1 to 2 amps, depending on the heater’s power output and fan speed. This makes diesel air heaters extremely efficient to run, especially for off-grid applications.
For example, a 2.2kW diesel heater can keep a caravan or RV warm all night on a low to medium setting, using just 10–20 amp-hours of battery capacity.
Most heaters also activate the glow plug again during shutdown to help clean it, which results in another short burst of higher power usage.
One of the most common causes of hard starting is low voltage due to poor wiring. Thin cables can cause excessive voltage drop, especially during startup. To avoid this, always connect the heater directly to your batteries, or use 6mm automotive cable on a dedicated circuit.
