What Size Heater Do I Need for My Camper Van or RV?
Most insulated camper vans need under 2 kW (about 6,800 BTU/h) to stay warm, even below freezing. Large or poorly insulated RVs in hard frost can need 3-6 kW. Estimate yours as volume × temperature difference × a loss factor, plus a 50 % margin, and check diesel heater claims with the 10 kWh-per-liter rule.
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Most insulated camper vans need under 2 kW (about 6,800 BTU/h) of heat, even below freezing. Large or poorly insulated RVs in hard frost can need 3-6 kW. The estimate is simple: interior volume × the temperature difference × a loss factor for your insulation, plus a 50 % margin to warm up quickly. The calculator below does it for you.
This guide explains the method, shows worked examples, and teaches the one check that exposes inflated diesel heater ratings.
How much heat does my camper need?
Heat needed = volume × (inside temperature − outside temperature) × a loss factor, then × 1.5 for warm-up. The loss factor is the heat your camper loses per cubic meter for each degree of difference, including air leaks. Our calculator uses three levels:
| Insulation | Loss factor (W per m³ per °C) | Typical build |
|---|---|---|
| Good | 1.5 | Closed-cell foam, double-glazed windows |
| Average | 2.5 | Factory insulation or a partly insulated van |
| Poor | 4 | Bare metal, single glazing |
The 1.5 multiplier gives you reserve to heat a cold van quickly. It is an estimate: thermal bridges, windows and wind all change the real result.
Use the heater size calculator
Pick your vehicle, set the coldest night and your target temperature, and choose your insulation level. The calculator uses metric units: enter volume in m³ and temperatures in °C.
Heat loss to cover: 0 W
Recommended output (with warm-up margin): 0 kW
Formula: W = volume × (inside − outside) × loss per m³ per degree. Recommended = W × 1.5. It is an estimate: thermal bridges, windows and wind change the result.
It returns two numbers. Heat loss to cover is what the heater must supply to hold the temperature. Recommended output is that loss × 1.5, in kW. It then suggests a heater class:
| Recommended output | What the calculator suggests |
|---|---|
| Up to about 2.2 kW | A 2 kW diesel heater is enough, or a 5 kW unit running on low |
| About 2.2 to 5 kW | A 4-5 kW diesel heater; a 2 kW unit would run flat out |
| Over 5 kW | Two heaters, or improve the insulation first |
The presets fill in typical volumes: a small van (6 m³), a large high-roof van like a Sprinter or Ducato (10 m³), a mid-size motorhome or Class B+ (18 m³) and a large motorhome, Class C or travel trailer (25 m³). The same tool is also on its own page as the heater size calculator.
What do real campers need? Worked examples
Even big RVs in hard frost rarely need more than 5 kW. All examples target 68 °F (20 °C) inside:
| Camper | Volume | Insulation | Outside | Heat loss | Recommended |
|---|---|---|---|---|---|
| Small van | 6 m³ (212 ft³) | Good | 23 °F (-5 °C) | 225 W | 0.34 kW (about 1,150 BTU/h) |
| Large van | 10 m³ (353 ft³) | Average | 23 °F (-5 °C) | 625 W | 0.94 kW (about 3,200 BTU/h) |
| Large van | 10 m³ (353 ft³) | Poor | 5 °F (-15 °C) | 1,400 W | 2.1 kW (about 7,170 BTU/h) |
| Mid-size motorhome | 18 m³ (636 ft³) | Average | 14 °F (-10 °C) | 1,350 W | 2.0 kW (about 6,910 BTU/h) |
| Large RV | 25 m³ (883 ft³) | Average | 5 °F (-15 °C) | 2,190 W | 3.3 kW (about 11,200 BTU/h) |
| Large RV | 25 m³ (883 ft³) | Poor | -4 °F (-20 °C) | 4,000 W | 6.0 kW (about 20,480 BTU/h) |
Notice how much insulation matters. The same 10 m³ van needs more than twice the heat when it is poorly insulated and 18 °F (10 °C) colder. Before buying a bigger heater, look at van insulation.
2 kW, 5 kW or 8 kW: which diesel heater class?
For most vans, a 5 kW heater on low or a 2 kW heater at mid power covers the need; 8 kW is rarely justified. All seven diesel heaters in our US catalog are sold at 5 kW or more.
| Class | Fits | Watch out for |
|---|---|---|
| 2 kW | Small and mid-size insulated vans | Runs flat out in a large or poorly insulated rig |
| 5 kW | Most vans on low, larger RVs at mid power | In a small van, it spends most time on minimum |
| 8 kW | Large, poorly insulated RVs, workshops | Oversized for vans; many 8 kW claims do not add up |
An oversized heater has a hidden cost. It reaches temperature, stops, cools down and restarts. Each start uses the glow plug’s current peak for a few minutes, and frequent starts use more battery and build more carbon. A minimum fuel setting matters more than a big maximum: the OBAKL OAH-B2’s 0.15 L/h low setting holds at most about 1.5 kW of fuel energy, which suits a small van.
How do I spot an inflated heater rating?
Multiply the heater’s maximum fuel use by 10: that is the most kW it can possibly deliver. One liter of diesel contains about 10 kWh of energy. No heater turns more than all of its fuel energy into heat, so the real output is below that figure.
- Find the maximum fuel consumption in L/h on the listing.
- Multiply by 10 to get the fuel energy in kW.
- Compare with the claimed output. If the claim is higher, it is impossible.
| Heater | Claimed | Max fuel | Fuel energy | Verdict |
|---|---|---|---|---|
| OBAKL OAH-B2 | 5 kW | 0.61 L/h | about 6.1 kW | Plausible |
| GEARLASSO DH004 | 8 kW | 0.45 L/h | about 4.5 kW | Impossible |
| DH Domestic Helper | 7 kW | 0.51 L/h | about 5.1 kW | Impossible |
| Hypothetical listing | 8 kW | 0.36 L/h | about 3.6 kW | Impossible |
If a listing gives no fuel figure, the rating cannot be checked. See how we treat each unit in the best diesel heaters, and estimate your nightly fuel and battery use with the diesel heater fuel calculator.
How do propane and electric heaters compare in size?
Convert everything to watts: W = BTU/h × 0.293. An electric heater turns its rated watts into heat, so a 1500 W unit gives about 5,120 BTU/h. A propane heater rated at 3,800 BTU/h gives about 1,110 W.
| Rating | In watts | In BTU/h |
|---|---|---|
| Electric heater, 800 W | 800 W | about 2,730 |
| Electric heater, 1500 W | 1,500 W | about 5,120 |
| Propane heater, 3,800 BTU/h | about 1,110 W | 3,800 |
| Propane heater, 9,000 BTU/h | about 2,640 W | 9,000 |
| Diesel heater, 5 kW | 5,000 W | about 17,060 |
On a hookup, electric heat is limited by amps: a 30 A RV hookup gives 3600 W in total. See the best electric space heaters for RVs and the best propane heaters.
What should I buy once I know the number?
Pick the heater type by where you camp, then the size by the calculator. Off-grid, a diesel heater in the 5 kW class running on low covers almost every van. On hookups, an electric heater of 800-1500 W handles mild to cool nights in a van. Our camper heaters hub compares the three types, and how to install a diesel heater covers the next step.
Frequently asked questions
Is a 2 kW diesel heater enough for a camper van?
For most insulated vans, yes. A 10 m³ (about 350 ft³) van with average insulation at 23 °F (-5 °C) needs under 1 kW with margin by our estimate. A 5 kW heater running on low does the same job with extra reserve.
Is an 8 kW diesel heater too big for a van?
Usually. It spends the night on its lowest setting and cycles on and off, which uses more battery and builds carbon. Also check the claim: 1 liter of diesel holds about 10 kWh, so a heater burning 0.45 L/h at most cannot make 8 kW.
How do I convert kW to BTU?
Divide watts by 0.293 to get BTU/h. So 1 kW is about 3,410 BTU/h, 2 kW about 6,830 BTU/h and 5 kW about 17,060 BTU/h. Propane heaters are usually rated in BTU/h, diesel heaters in kW.
How do I measure my van’s interior volume?
Multiply the inside length, width and height of the living space. In feet, divide cubic feet by 35.3 to get cubic meters: a 12 × 5.8 × 6 ft space is about 418 ft³, or 11.8 m³.
What if the calculator says I need more than 5 kW?
Improve insulation first: it lowers the heat you need every night. If that is not possible, consider two heaters rather than one oversized unit, so each can run in its efficient range.