Diesel Heater Fuel Calculator: Fuel and Battery Use Per Night
Pick a 2, 5 or 8 kW preset or enter your heater’s fuel and power range, the average output, hours per day and tank size. With the defaults, a 5 kW heater at 35 % for 10 hours burns about 3.2 L (0.85 gal) and uses about 17 Ah at 12 V.
This calculator estimates how much diesel your heater burns per day, how many days the tank lasts and how much it takes from your battery. Pick a 2, 5 or 8 kW preset, or type the minimum and maximum fuel use and power draw from your heater’s listing. Then set the average output, hours per day, tank size and battery voltage.
Fuel inputs are in liters (1 US gallon ≈ 3.785 L).
Fuel per day: 0 l · tank lasts 0 days
Battery per day: 0 Ah (0 Wh)
Formula: average L/h = min + (max − min) × % output; Ah = average W × hours ÷ voltage. Excludes the glow-plug peak at start-up (a few minutes at 100 W or more).
How does the calculation work?
It interpolates between your heater’s minimum and maximum, then multiplies by the hours.
- Average fuel (L/h) = minimum + (maximum − minimum) × average output %.
- Fuel per day = average L/h × hours on. Days per tank = tank ÷ fuel per day.
- Average power (W) = minimum W + (maximum W − minimum W) × average output %.
- Battery per day = average W × hours = Wh; Wh ÷ battery voltage = Ah.
The presets are typical ranges: 2 kW (0.12-0.26 L/h, 10-36 W), 5 kW (0.16-0.62 L/h, 10-40 W) and 8 kW (0.18-0.72 L/h, 10-50 W). Replace them with your heater’s own figures when you have them.
Example, the defaults: a 5 kW heater at 35 % for 10 hours with a 5 L tank on 12 V. Fuel: 0.16 + 0.46 × 0.35 ≈ 0.32 L/h, so about 3.2 L (0.85 gal) a day and about 1.6 days per tank. Power: 10 + 30 × 0.35 = 20.5 W, so 205 Wh or about 17 Ah.
The result excludes the glow plug peak at start-up, a few minutes at 100 W or more.
How do I read the result?
Check the battery figure against your usable capacity, and the fuel figure against your tank and refueling plans.
| Result | What it means | What to do |
|---|---|---|
| Under 20 Ah a day at 12 V | Easy for most house batteries | Nothing; avoid frequent restarts |
| 20-40 Ah a day | Fine with solar or daily driving | Run on low rather than cycling on and off |
| Over 40 Ah a day | Heavy for a small battery | Size your battery with the RV power calculator |
| Tank lasts under 2 days | Frequent refills | A larger tank; ask your installer about the options |
| Output near 100 % all night | Heater too small for the rig | Re-check with the heater size calculator |
You can also use the result to spot inflated ratings. A liter of diesel holds about 10 kWh, so maximum fuel use × 10 is the most heat a heater can make. A heater that burns at most 0.26 L/h cannot exceed about 2.6 kW, whatever the box says. Our ranking of the best diesel heaters checks each listing this way.
Frequently asked questions
How much diesel does a camper heater use per night?
It depends on the output you run it at. With the calculator’s defaults, a 5 kW heater at 35 % output burns about 0.32 L/h, or 3.2 L (about 0.85 gal) over 10 hours. A 2 kW heater on low burns much less.
How many amp-hours does a diesel heater use?
Running, not much: the presets assume 10 to 36-50 W. At the defaults, about 20.5 W for 10 hours is 205 Wh, or about 17 Ah at 12 V. Start-up adds a glow plug peak that the calculator does not include.
What average output percentage should I enter?
Use 20-40 % for a well-insulated van on a mild night and more in hard frost or a poorly insulated rig. If your heater runs flat out all night, it is probably too small; check with the heater size calculator.
Why does starting and stopping the heater drain my battery?
At start-up, the glow plug draws a current peak for a few minutes, often 100 W or more. Frequent starts use more battery and cause more carbon build-up than running continuously on low.
Does the calculator work in gallons?
Its inputs are in liters. Divide liters by 3.785 to get US gallons, or multiply your tank’s gallons by 3.785 before entering it.