Preventing Condensation in UK Winter — Van Life Guide
Why Condensation Is the Enemy
Condensation is the single biggest moisture problem in a UK campervan. It forms when warm, moist air inside the van hits cold surfaces — windows, metal panels, roof lining — and the water vapour condenses into liquid. Left unchecked, it leads to mould, damp insulation, rust, rotting wood, and a persistent musty smell that is almost impossible to remove.
The UK is particularly bad for condensation because of our climate: high humidity, frequent rain, and cold winters mean the air inside a van is constantly moisture-rich. Cooking, breathing, and drying clothes add more moisture. A person exhales about 1 litre of water vapour per night through breathing alone. Two people in a closed van = 2 litres of water settling on surfaces every night.
How Condensation Forms in a Van
The process is simple physics. Warm air holds more moisture than cold air. When warm air from your body, your cooking, or your heater hits a cold surface like a window or an uninsulated metal panel, it cools rapidly and releases that moisture as liquid water.
The worst areas are:
- Windows — glass is the coldest surface in the van
- Roof panels — heat rises but the roof is exposed to cold outside air
- Wheel arches — thin metal directly exposed to road spray
- Cab doors — the gap between cab and living area lets warm air reach cold metal
Prevention Strategy
There is no single cure for condensation. You need a combination of three approaches: reduce moisture at source, ventilate effectively, and manage surface temperatures.
1. Reduce Moisture at Source
Cooking — Always use a lid on pans. A pan without a lid releases most of its water into the van air. A lid keeps it in the pan and reduces condensation by about 60%. If you have a hob with an extractor, use it. Otherwise, crack a roof vent or window while cooking.
Drying clothes — Never dry wet clothes inside a closed van. A set of jeans and a jumper holds about 500ml of water. Drying them inside adds that much moisture to the air. Use a heated clothes airer designed for 12V (about £30) but run it with the roof vent open. Better yet, hang clothes outside on a line or awning rail.
Breathing — You cannot stop breathing, but you can manage the moisture. A roof vent cracked open overnight allows moist air to escape. In winter, run your diesel heater on low continuously rather than letting the van get cold and reheating it — constant low heat keeps surfaces above the dew point.
Propane/gas cooking — Propane combustion produces about 1.5L of water vapour per kg of gas burned. This is a significant moisture source. Ventilate aggressively when cooking on gas. If you cook a lot, consider an induction hob running off your leisure battery — it produces no combustion moisture.
2. Ventilate Properly
Ventilation is the most effective tool against condensation. You need airflow that removes moist air and replaces it with drier outside air.
The minimum setup:
- One roof vent (MaxxAir or equivalent) extracting air at low speed continuously
- One lower vent (cab window cracked or a floor-level vent) letting fresh air in
This creates a airflow path: cool dry air enters at the bottom, warms up, picks up moisture, and exits through the roof. Even in winter, running the roof vent on low (speed 1-2) removes significant moisture without making the van too cold.
The MaxxAir advantage — MaxxAir roof fans have a built-in thermostat and can be set to run continuously at low speed. They also have a rain sensor that closes the vent if it starts raining. Running one on speed 1 overnight removes condensation without freezing you out.
Window moisture — If you wake up to running water on the windows, your ventilation is insufficient. Increase the fan speed or crack an additional window.
3. Manage Surface Temperatures
When surfaces are below the dew point, condensation forms on them. The solution is to either insulate the surface (so it stays warmer) or keep the van interior above the dew point.
Insulation layering — Vapour barrier is critical. If you have a vapour-permeable insulation layer (rockwool, sheep's wool, fibreglass), warm moist air can pass through it and condense on the metal skin behind it. This creates hidden rust. Use closed-cell foam (CCF) or a dedicated vapour barrier sheet between the insulation and the metal.
Windows — Single-glazed windows are the worst. If you cannot afford double glazing, use insulated window covers at night. Reflectix or similar bubble-foil material cut to window size and held in place with suction cups reduces heat loss through glass by about 70% and stops condensation on the glass.
Diesel heater — Running a diesel heater on low continuously keeps the interior temperature above the dew point. Set it to 10-12°C overnight. This uses about 0.1-0.2L of diesel per hour and is far more effective than heating up from freezing every morning.
What to Avoid
Avoid leaving wet items in the van — Wet towels, swimsuits, and coats left on surfaces add moisture all night. Hang them in the cab (over the seats) with a window cracked or put them in a mesh bag in the roof vent's airflow.
Avoid sealing the van too tightly — A common mistake is to seal every gap for warmth. But a sealed van traps moisture. You need controlled airflow, not zero airflow.
Avoid open flames — Unflued gas heaters and candles produce massive amounts of water vapour. A single candle releases about 10g of water per hour. A gas catalytic heater releases about 150g per hour. Do not use these as primary heat sources in a van.
Gear That Helps
| Item | What It Does | Price |
|---|---|---|
| MaxxAir Deluxe roof fan | Continuous low-speed extraction, rain sensor | £180-220 |
| Insulated window covers (Reflectix) | Stops glass condensation, reduces heat loss | £15-30 DIY |
| 12V heated clothes airer | Dries clothes with vent open | £30-40 |
| Small dehumidifier (12V) | Removes moisture from air (less effective than ventilation) | £40-80 |
| Moisture absorber bags (silica gel) | Absorb small amounts in cupboards | £5-10 |
| Mesh laundry bags | Dry items in airflow without contact | £3-5 |
The Bottom Line
Condensation in a UK van is manageable if you understand how it works. The three-pronged approach — reduce moisture at source, ventilate continuously, and keep surfaces warm — eliminates 90% of condensation problems.
The single best investment is a MaxxAir roof vent running on low overnight. It costs about £200 and makes more difference to winter van comfort than any other piece of equipment.
My recommendation: Install a MaxxAir fan before winter. Run it on speed 1 overnight with a low setting on your diesel heater. Use insulated window covers. You will wake up to dry windows and a comfortable van.
