Quick answer: an Airrex AH-500i uses 1,05 l/h on LOW (11 kW) and 1,42 l/h on HIGH (15 kW). An Airrex AH-900i uses 1,81 l/h on LOW (19 kW) and 2,3 l/h on HIGH (24 kW). These are full-output figures. Once the building is warm, the automatic thermostat runs the burner only in short cycles, and daily consumption in an insulated hall can drop to a few litres.
Fuel consumption per model
| Model | Output LOW / HIGH | Fuel use LOW / HIGH | Tank | Run time on one tank (full output, LOW / HIGH) | Electricity |
|---|---|---|---|---|---|
| Airrex AH-500i | 11 / 15 kW | 1,05 / 1,42 l/h | 45 l | approx. 43 h / 32 h | 50 W (230 W for about 30 s at start-up) |
| Airrex AH-900i | 19 / 24 kW | 1,81 / 2,3 l/h | 70 l | approx. 39 h / 30 h | 60 W (230 W for about 30 s at start-up) |
How much diesel does a heater use per day in practice?
Much less than the hourly figure × 24. The thermostat switches the burner off when the set temperature is reached and on again when it drops. Documented example: an insulated 500 m³ industrial hall kept at +15 °C with 0 °C outdoors uses about 2,5 litres of diesel per day for maintenance heating. A customer heating an insulated 1 080 m³ hall reported annual fuel use falling from about 2 500 litres of oil with radiators and fan heaters to about 1 000 litres with an Airrex infrared heater. Read the case: steady warmth and real savings.
What affects consumption most?
- Insulation and doors. A sealed, insulated building needs a fraction of the fuel an open or uninsulated one needs.
- Target temperature. Keeping a hall at +10 °C and raising it to +15 °C only during working hours saves fuel compared with +18 °C around the clock.
- The first week. Consumption is higher during the first one to two weeks because walls and floors absorb heat and moisture dries out. After that the structures act as a heat store and consumption stabilises.
- Output setting. Dual Power lets you run on LOW when full power is not needed.
- Infrared versus hot air. Infrared heats objects and people directly instead of heating air that rises to the ceiling, so the heat stays at working height and recovers quickly after a door is opened.
Which fuel can I use?
Renewable diesel HVO100 (EN 15940) or standard diesel (EN 590). HVO100 is made from waste and residue raw materials and burns cleanly; the Blue Flame burner gives complete combustion with ultra-low emissions and no odour in normal operation. Read more: heating with renewable diesel.
How much electricity does a diesel infrared heater need?
Only 50 W (AH-500i) or 60 W (AH-900i) while running, plus about 230 W for roughly 30 seconds during fuel pre-heating at start-up. There is no fan, which is why the power draw is so low. A standard 230 V, 50 Hz single-phase socket is sufficient.
Does maintenance affect consumption?
Yes. A clean nozzle and fuel filter keep combustion complete and consumption at the rated level. We recommend an annual service with the original Airrex service kit; it is also a condition of the extended 5-year warranty (2 years standard + 3 years on registration). See service kits and spare parts.
Which model do I need for my space?
AH-500i for spaces up to 1 500 m³, AH-900i for spaces up to 2 500 m³. Use the diesel heater sizing guide to calculate your space and see worked examples, or ask Rex Nordic for a recommendation.
Safety note: Airrex heaters must never be used in rooms where people sleep. Ensure adequate supply air; an exhaust pipe can be fitted to lead combustion gases outdoors.