Campervan Heating Calculator
2kW, 4kW or 6kW Heater?
Calculate the exact heating output required based on your van volume, insulation levels, and travel destinations.
🚐 Vehicle Size & Insulation
🌡️ Travel & Weather Conditions
Campervan Heating: Why Calculate Required Output?
Installing a diesel auxiliary heater is a crucial step for year-round vanlife. However, most first-time builders make the mistake of buying an oversized heater, assuming more output automatically guarantees better comfort. Using a heating calculator allows you to accurately estimate your thermal requirements, preventing carbon soot build-up inside the combustion chamber and optimizing fuel consumption.
The 3 Pillars of an Accurate Thermal Assessment
To correctly size your Autoterm, Webasto, Eberspächer, or Chinese diesel heater, three core variables govern thermodynamic heat loss in a leisure vehicle:
- Living space volume: Heating a short wheelbase van (VW T6, Transit Custom) naturally requires less than half the energy of a long wheelbase, high-roof panel van (Mercedes Sprinter L3H2 or Fiat Ducato L4H3).
- Insulation rating (G-Factor): Proper closed-cell insulation (Armaflex, Dodo Mat) retains heat efficiently. Uninsulated steel panels, thermal bridges, and unmasked windows act as severe heat sinks.
- Temperature differential: Maintaining 20°C indoors when it is 5°C outside requires moderate output. Facing sub-zero UK winter freezes or Scottish Highland conditions at -15°C demands a completely different thermal budget.
The Mechanical Trap of an Oversized 4kW Heater
Why not simply fit a 4000-Watt heater just in case? Diesel heaters need to run periodically on medium-to-high settings to burn off carbon deposits. If you fit a 4kW unit inside a small 10 m³ space, the cabin reaches temperature in minutes, forcing the heater to idle continuously on its lowest power setting.
- The consequence: The combustion chamber clogs up rapidly with heavy carbon soot.
- The symptoms: Thick white smoke, glow plug failure, and complete shutdown during a freezing winter trip.
- The solution: A 2kW (2000W) heater runs hotter and cleaner, making it far more reliable for 90% of campervan conversions.
Optimising Winter Comfort & Safety On the Road
To ensure your heating installation is both efficient and compliant with UK build guidelines, raw wattage is only part of the equation:
- Maintain fixed BS EN 721 permanent ventilation to expel humidity and moisture caused by breathing and cooking.
- Select a heater model equipped with a high-altitude sensor/kit if you plan to travel through mountain passes over 1,500 metres.
- Position the warm air outlet centrally, ensuring furniture or bedding does not obstruct the direct airflow.
Heater size decided? Discover how to install your heating system safely, prevent frozen water lines, and stay warm in extreme cold in our complete guide.
FAQ: Insulation & Auxiliary Campervan Heating
Should I choose a 2kW or 4kW diesel heater for my van?
If you are converting a standard panel van (up to MWB/LWB High Roof) with good insulation (such as 19mm Armaflex or Dodo Mat), a 2kW (2000W) diesel heater is ideal. It will run at a high enough setting to prevent carbon soot build-up. A 4kW heater is strictly reserved for extra-large volumes (Luton box vans, XLWB Maxi vans) or uninsulated vehicles.
What is diesel heater carbonisation (sooting up)?
An auxiliary diesel heater needs to run periodically at medium-to-high power to burn off the carbon soot generated during fuel combustion. If oversized, the heater will constantly idle on its lowest setting, rapidly clogging the combustion chamber with carbon, emitting white smoke, and eventually locking out completely.
Where is the best place to install a diesel heater in a van?
The ideal location is close to the vehicle's fuel tank to avoid an excessively long fuel line (most commonly mounted under the passenger seat base or centrally under the floor). The warm air outlet must blow freely into the main walkway without obstruction from furniture.
Can I use a portable unvented gas heater inside a campervan?
No, this is extremely dangerous and potentially lethal. Unvented portable gas heaters (catalytic heaters) release carbon monoxide (an odourless, deadly gas) and huge amounts of moisture directly into the living space, causing severe condensation and immediate health risks.
What is an altitude kit (mountain mode)?
Above 1,500 metres in altitude, thin air lacks oxygen. If a diesel heater continues injecting standard fuel amounts, the air-fuel mixture becomes rich, causing the unit to soot up in a matter of days. An "altitude kit" (built into modern controllers) automatically reduces the fuel pump frequency to compensate for reduced oxygen levels.
Does a diesel heater use a lot of battery power?
Only during initial startup! To glow the internal spark plug, the heater can draw between 10 and 15 Amps for about 2 minutes. Once the flame is established, electrical consumption drops drastically to around 1 to 2 Amps to power the internal fan.
How much diesel does a campervan heater consume?
It is extremely economical. A 2kW unit (like an Autoterm 2D or Webasto Air Top) consumes between 0.1 and 0.25 litres of diesel per hour of continuous operation depending on output setting. Expect to use around 1 to 2 litres of fuel maximum over a full winter night.
Why does my van still suffer from condensation when the heater is on?
Heating warms the air, but if your van lacks fixed ventilation (skylights sealed, drop vents missing), the moisture generated by your breathing and cooking will condense on cold metal surfaces. You must maintain permanent fixed airflow (BS EN 721 compliant) even in sub-zero winter weather.
Are cheap "Chinese Diesel Heaters" reliable?
Popular budget diesel heaters work on the exact same thermodynamic principle as premium brands. They produce excellent heat, but rely on cheaper internal components, noisier fuel pumps, and less reliable temperature sensors. While widely used by UK DIY builders, ensure they feature a valid CE marking and robust exhaust fitting to pass insurance requirements.
Will a diesel heater pass a Gas Safe or safety inspection?
Yes, provided it holds European E-mark / CE safety certification (ECE R122 for heating appliances). The installation must strictly follow manufacturer safety guidelines, including a sealed turret plate passing through the floor, sealed exhaust routed safely away from living areas under the chassis, and adequate clearance from combustible materials.
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