Camper Van in Winter: Heating, Insulation, Condensation, and Freezing

What a warm night uses

0.03 gallons (0.12 liters) of diesel an hour. That’s the lowest fuel consumption Webasto lists for its Air Top 2000 STC, a 3,100 to 7,000 BTU/h (0.9 to 2 kW) air heater the company markets for truck cabs and sleeper bunks [1]. At full output, it burns twice that: 0.06 gallons (0.24 liters) an hour. Let’s do the math for a 12-hour winter night: roughly 0.4 to 0.8 gallons (1.5 to 3 liters) of diesel.

A combustion heater also uses electricity to run its fans and electronics: 14 to 29 W according to the same spec sheet, or 15 to 29 Ah over a 12-hour night on a 12 V system [1]. On propane, the Truma Combi 4, which heats both the living space and the water, lists 0.35 to 0.74 lb (160 to 335 g) of fuel per hour for 2 or 4 kW, and an average current draw of about 1.2 A [2]. Over 12 hours, that’s 4.4 to 8.8 lb (2 to 4 kg) of propane and about 14 amp-hours.

For a weekend of snowshoeing or cross-country skiing, meaning two nights, the diesel heater needs 0.8 to 1.6 gallons (3 to 6 liters) of diesel and 30 to nearly 60 Ah.

On paper, an electric space heater running off the house battery would solve everything: no fuel, no exhaust. The math knocks that idea 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’d need nearly 19 of them, plus a current of more than 150 A to deliver those 2 kW. Electricity heats a van beautifully when it’s plugged into a campground hookup, never when it’s running on a battery.

The heater’s amp-hours add to those of the fridge, the lights, and everything else. That’s exactly what our guide to sizing your house battery is for: a power budget worth redoing for winter, when short days also cut into solar charging.

Diesel, propane, or portable: which heater for overnight

Permanently installed heaters, diesel or propane, are designed to run all night. In Truma’s design, for example, combustion air comes in from outside through a flue, and the exhaust gases leave to the open air through that same flue; the air in the living space warms up as it passes over a heat exchanger [2]. That separate circuit is what makes the appliance safe, as long as it’s installed according to the manufacturer’s instructions and maintained. I recommend having a professional install it: one badly connected duct, and the separate circuit is gone.

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A portable heater is a different story. Santé publique France, France’s national public health agency, recommends never running one for more than two hours at a stretch, and lists these heaters, when misused, among the leading causes of carbon monoxide poisoning [3]. So a small propane heater sitting on the floor will warm an evening, not a night. Without a flue, it also releases the water vapor from its combustion into the van: 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 die [3]. The gas is invisible, odorless, and nonirritating: nothing tips you off. Santé publique France lists among the main causes flue-connected appliances that are poorly maintained or badly adjusted, and portable appliances that are misused [3].

RVs are named outright in its recommendations: generators, braziers, and grills should never be used in an enclosed space, or even near doors, windows, or vents. Cooking appliances, propane stoves included, should never be used for heat. And you should air out the space for at least ten minutes a day, even in cold weather, without ever blocking the vents [3].

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

Insulation: where the van loses its heat

Poorly insulated metal walls and the windows are the coldest surfaces inside the van. That’s where the heat escapes, and that’s where water collects: insulating both saves on heating and limits condensation.

The best-value fixes don’t require tearing out the build: insulated covers on the windshield and windows, a heavy curtain between the cab and the living area so you only heat the space you live in, and a rug on the floor. One limit, though: insulating never means sealing the van up. The vents stay open, and the air moving through also carries moisture away.

The last layer of insulation is your bed. A sleeping bag rated for the right temperature lets you turn the thermostat down at night, and with it the heater’s consumption.

Condensation: where the water on the windows comes from

Condensation isn’t a leak: it’s water vapor in the air turning back into liquid when it touches a cold surface. In a closed-up van, that vapor 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 takes hold, mold follows in poorly ventilated corners, behind cushions or under the mattress.

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The fixes follow from the cause: get the moisture out, make less of it, and warm up the cold surfaces.

• Air out the van for at least ten minutes a day, even when it’s freezing, as Santé publique France recommends [3].
• Open the roof vent or a window while you cook, and keep a lid on the pot.
• Dry wet clothes outside or in a closed bag, not over the heater.
• Put insulated covers on the windows: the less cold they are, the less water they collect.
• Leave room for air to circulate under the mattress and behind the cushions.

Water and freezing: protecting tanks and water lines

Water freezes at 32 °F (0 °C) and expands as it does: a full line can split, a pump can crack. The first parts to freeze are the ones left outside: a tank under the floor, a drain valve, a hose running along the body.

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Some water heaters protect themselves. On Truma units, the FrostControl drain valve opens below 37 °F (3 °C) and automatically empties the water heater, in bursts, so the outlet doesn’t freeze [6]. Finding the water heater empty on a frosty morning isn’t a malfunction: it means the protection did its job.

When the van sits unheated in freezing weather, the safest move is to drain the whole system, tanks, lines, and pump included, following your van builder’s instructions. On the road, keep drinking water in bottles, inside the van.

Batteries in the cold: discharge yes, charge no

The last trap is the sneakiest: the lithium battery. Victron, for example, rates its Smart lithium iron phosphate batteries for discharge from -4 to 122 °F (-20 to +50 °C), but for charging only from 41 to 122 °F (+5 to +50 °C). Since a 2018 update, its battery management system has blocked charging below 41 °F (5 °C), because charging at lower temperatures speeds up wear [7].

In an ice-cold van, a battery like that can power the heater all night, then refuse a charge from the solar panel or the alternator in the morning until it warms up. The fix takes one line in the build plan: the battery goes inside the heated space, not in an outside compartment. Thresholds vary from one manufacturer to another: only your own battery’s spec sheet counts.

In winter, a camper van gets heated with an appliance built for overnight use, a carbon monoxide alarm, and open vents, or it doesn’t get heated at all.

Julien de Jurquet

Vans, RVs, biking and calculators

Julien de Jurquet writes for Outfarer about camper vans, RVs, biking, and calculators. He reads manuals cover to cover and never lets a number slide without its unit, so your choices rest on math, not promises.

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