Heat loss & heater size calculator
A van loses heat through 30 m² of thin steel, a wall of cab glass and the air it has to breathe. This adds the three up at the temperature you actually camp in and tells you which heater class you need — and what a night of it burns.
Pick your van and the numbers below fill themselves from a database of 159 variants.
The cargo box behind the cab: between the walls, floor to ceiling. Pick a van above and these fill themselves.
Insulation per surface
Floor
Walls + rear doors
Ceiling
Windscreen and cab doors alone are ~2.5 m²; add every habitation window. Curtains and cab covers do not change the figure much.
Heat loss
1 262 W
In BTU/hr
4 306 BTU/hr
Heater class
2 kW
Per 8-hour night
10.1 kWh
Diesel ≈ 1.2 L · LPG ≈ 0.9 kg · Electric at 12 V ≈ 841 Ah
2 kW — the small diesel or gas air heater (Airtronic D2, Propex HS2000 class)
Where it goes
- Floor131 W
- Walls + doors456 W
- Ceiling184 W
- Glazing435 W
- Ventilation55 W
34 % of the loss goes through the glass. Insulating the walls further changes little until the cab is curtained off with an insulated divider.
Summer check: the same glass in full sun brings in about 2364 W — more than most heaters put out. Shade it before you size air conditioning.
The VanPlot Build Sheet computes this from the exact shell — every window and roof fan you cut out, the insulation and lining you specified — and reports the heater class next to your power budget.
Size the heater for your real layout — free →Planning figures, not certification. Standards are summarised for builders; your inspector, your van's plate and your own measurements always win.
How this is calculated
- Shell loss = Σ (area ÷ R) × ΔT per surface, with R = 0.18 m²K/W for bare steel and air films + insulation thickness ÷ λ. Areas come from the van's interior box (floor, two walls plus rear doors, ceiling).
- Glazing loss = glass area × U × ΔT with U = 5.8 W/m²K for single glass and 3.0 for double-skin acrylic. Ventilation loss = 0.33 × air changes per hour × cabin volume × ΔT — the metric form of 1.08 × CFM × ΔT.
- Heater class from the total: up to 1.7 kW → 2 kW unit; up to 3.3 kW → 4 kW; above → 5–6 kW. A night is 8 hours at steady state; diesel at 9.9 kWh/L and 85 % efficiency, LPG at 12.8 kWh/kg and 90 %.
Sources
- Build A Green RV — camper van heat loss calculator (Σ(A/R)×ΔT + 1.08×CFM×ΔT) and measured insulation tests
- EN 721:2019 — ventilation air-change assumptions
- Eberspächer, Webasto and Propex heater datasheets (rated outputs)
Questions builders ask
What size heater do I need for a camper van?
A 2 kW diesel or gas air heater (Eberspächer Airtronic D2, Webasto Air Top 2000, Propex HS2000) covers a mid-size or insulated high-roof van down to about −5 °C: with 25 mm insulation, 3 m² of glass and normal ventilation a Ducato L3H2 loses roughly 1.3 kW at −5 °C outside. Uninsulated, the same van loses almost 5 kW and needs the 5–6 kW class.
How much diesel does a van heater use per night?
About 0.1–0.2 L per hour on a cold night: 1.5 kW of heat loss over 8 hours is 12 kWh, which is roughly 1.4 L of diesel at 85 % efficiency, or about 1 kg of LPG. The same night from a 12 V battery would be 1,000 Ah — which is why nobody heats a van electrically off-grid.
How much heat does a van lose uninsulated?
Around 4–5 kW at −5 °C for a high-roof van: 31 m² of bare steel at R 0.18 m²K/W loses about 4.3 kW across a 25 K difference before glass and ventilation are counted. 25 mm of XPS or PIR cuts the shell loss by 81–86 %; the second 25 mm only removes another 8–9 %.
Keep reading
Plan the whole van, not just this number
VanPlot is a 3D layout planner for camper conversions. Place real components in your real van and watch weight, axle loads, power and cost update live — this calculator is one panel of it.
Who makes this
I'm Vladimir. I'm planning my own conversion, and none of the tools I tried could tell me whether a layout would fit or what it would do to the rear axle, so I made this one. I work on it alone. If something's wrong or missing, write to me — the address goes to my inbox.
Vladimir Šterjoski