Campervan in winter: heating, insulation, condensation and frost

What a warm night consumes

0.12 litres of diesel an hour. That is the lowest consumption Webasto quotes for its Air Top 2000 STC, a 0.9 to 2 kW air heater that the manufacturer’s US website markets for lorry cabs and sleeper bunks [1]. Flat out, it burns twice as much: 0.24 litres an hour. Let’s do the maths for a 12-hour winter night: between 1.5 and 3 litres of diesel.

A combustion heater also uses electricity, for its fans and electronics: 14 to 29 W according to the same data sheet, or 15 to 29 Ah over a 12-hour night on a 12 V system [1]. On gas, the Truma Combi 4, which heats both the living space and the water, quotes 160 to 335 g of gas an hour for 2 or 4 kW, and an average current draw of about 1.2 A [2]. Over 12 hours, that makes 2 to 4 kg of gas and about 14 amp-hours.

For a weekend of snowshoeing or cross-country skiing, which means two nights, the diesel heater therefore needs 3 to 6 litres of diesel and 30 to almost 60 Ah.

On paper, an electric heater running off the leisure battery would solve everything: no fuel, no exhaust gases. The calculation rules it out in two lines. 2 kW for 12 hours is 24 kWh. A 100 Ah lithium battery at 12.8 V stores 1.28 kWh: you would need almost 19 of them, and a current of more than 150 A to deliver those 2 kW. Electricity heats a campervan very well on a campsite hook-up, never on a battery.

The heater’s amp-hours come on top of those for the fridge, the lights and everything else. That is the whole point of our guide to sizing your leisure battery: a power budget worth redoing for winter, when short days also cut solar charging.

Diesel, gas or portable: which heater for the night

Fixed heaters, whether diesel or gas, are designed to run through the night. On a Truma heater, for example, combustion air comes in from outside through a flue, and the exhaust gases leave into the open air through that same flue; the air in the living space warms up as it passes over a heat exchanger [2]. This separate circuit is what makes the appliance safe, provided it is installed according to the manufacturer’s instructions and serviced. I would recommend having it fitted by a professional: one badly connected duct, and the separate circuit no longer exists.

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A portable heater is in a different category altogether. Santé publique France, the French national public health agency, advises never running one for more than two hours at a time, and lists these appliances, when misused, among the main causes of carbon monoxide poisoning [3]. A small gas heater standing on the floor will therefore warm an evening, not a night. With no flue, it also releases the water vapour from its combustion into the living space: more on that below.

Carbon monoxide: alarm, ventilation and warning signs

Every year in France, around 3,000 people are accidentally poisoned by carbon monoxide, and about a hundred of them die [3]. The gas is invisible, odourless and non-irritating: nothing gives it away. Santé publique France names among the main causes flue-connected appliances that are poorly maintained or badly adjusted, and portable appliances that are misused [3].

Motorhomes are named explicitly in its recommendations: generators, braziers and barbecues must never be used in an enclosed space, nor even near doors, windows or vents. Cooking appliances, gas stoves included, must never be used for heating. And you should air the space for at least ten minutes a day, even in cold weather, without ever blocking the vents [3].

That leaves the alarm. One European standard specifically covers carbon monoxide alarms installed permanently in recreational vehicles and boats: EN 50291-2, in its 2019 version [5]. I count the alarm as part of the heating, just like the flue: look for this reference on the packaging or in the instructions, and install the alarm as its manufacturer specifies.

Insulation: where the van loses its heat

Poorly insulated metal panels and the windows are the coldest surfaces in the living space. That is where the heat escapes, and that is where water settles: insulating therefore both saves on heating and limits condensation.

The most cost-effective measures do not involve stripping out the conversion: insulating screens on the windscreen and windows, a thick curtain between the cab and the living area so that you only heat the space you live in, and a rug on the floor. One limit, though: insulating never means sealing up. The vents stay open, and the circulating air also carries the moisture away.

The last layer of insulation is the bed. A sleeping bag chosen for the right temperature lets you turn the heating down at night, and so reduce its consumption.

Condensation: where the water on the windows comes from

Condensation is not a leak: it is water vapour in the air turning back into liquid on contact with a cold surface. In a closed van, that vapour comes from you. Breathing, cooking and wet clothes drying all load the air with water, and a heater without a flue adds the water from its combustion. Once condensation sets in, mould follows in poorly ventilated corners, behind cushions or under the mattress.

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The remedies follow from the cause: remove the moisture, produce less of it, and warm up the cold surfaces.

• Air the van for at least ten minutes a day, even when it is freezing, as Santé publique France recommends [3].
• Open the roof vent or a window while cooking, and cook with a lid on.
• Dry wet clothes outside or in a closed bag, not above the heater.
• Fit insulating screens to the windows: the less cold they are, the less water they collect.
• Leave an air gap under the mattress and behind the cushions.

Water and frost: protecting tanks and pipes

Water freezes at 0 °C and expands as it does: a full pipe can split, a pump can break. The first parts to freeze are those left outside: a tank under the floor, a drain valve, a pipe running along the bodywork.

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Some water heaters protect themselves. On Truma models, the FrostControl drain valve opens below 3 °C and empties the water heater automatically, in bursts, so that the outlet does not freeze [6]. Finding the water heater empty on a frosty morning is therefore no breakdown: it means the protection has worked.

When the van is left unheated in freezing weather, the safest course is to drain the whole system, tanks, pipes and pump included, following the converter’s instructions. On the road, keep drinking water in bottles, inside the van.

Batteries in the cold: discharging yes, charging no

The last trap is the least obvious: the lithium battery. Victron, for example, allows its Smart lithium iron phosphate batteries to be discharged from -20 to +50 °C, but charged only from +5 to +50 °C. Since an update in 2018, its management system has blocked charging below 5 °C, because charging at lower temperatures speeds up wear [7].

In an ice-cold van, a battery like this can therefore power the heater all night, then refuse in the morning to take a charge from the solar panel or the alternator until it has warmed up. The fix fits in one line of the conversion plan: the battery goes inside the heated space, not in an outside locker. Thresholds vary from one manufacturer to another: only your own battery’s data sheet counts.

In winter, a campervan is heated with an appliance designed for the night, a carbon monoxide alarm and open vents, or it is not heated at all.

Julien de Jurquet

Campervans, motorhomes, cycling and calculators

Julien de Jurquet writes for Outfarer about campervans, motorhomes, cycling and calculators. He reads instruction manuals to the very end and never lets a figure through without its unit, so that your choices rest on sums rather than promises.

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