Winter Caravan Storage: Should You Leave a Heater On?
The short answer is no, not a portable fan heater, and in most cases not at all. Almost every storage site in the UK prohibits unattended electrical appliances, many do not supply electricity to individual pitches, and an unattended heater in an unoccupied caravan is a fire risk with nobody there to notice.
The instinct behind the question is sound, though. Keeping a stored caravan above the dew point really does prevent condensation and mould. There are just better ways to achieve it than leaving a fan heater running for four months.
Why people ask
Condensation forms when warm, moist air meets a surface colder than its dew point. In a sealed caravan sitting through a British winter, the air inside is damp and every surface is cold, so moisture settles on the walls, the window frames and the undersides of cushions. Over a few months that becomes black mould, a musty smell that is very difficult to remove, and in bad cases damage to soft furnishings and trim.
Frost damage is the other worry: water left in pipes freezes, expands and splits fittings.
Both problems are real. Neither is best solved with a heater.
Solve the frost problem by draining, not heating
Frost damage is entirely preventable and costs nothing. Drain the fresh tank, drain the water heater, open all the taps to the mid position, drain the waste tank, remove the submersible pump, and empty the toilet cassette. If there is no water in the system there is nothing to freeze.
Trying to keep a caravan above freezing all winter with a heater is an expensive way to protect pipes you could simply have emptied. Our winter preparation checklist covers the full drain-down sequence.
Solve the damp problem with airflow first
Ventilation does most of the work, and it costs nothing at all.
- Never block the fixed roof and floor vents. They are what stops the van becoming a sealed damp box.
- Stand seat cushions on edge, or take them home entirely.
- Leave wardrobe and locker doors ajar so air moves behind them.
- Prop the fridge door open on its catch.
- Remove all bedding, towels and fabric.
- Put moisture traps in and check them when you visit. They fill faster than expected.
- Use a breathable caravan cover, not a tarpaulin. A non-breathable cover traps moisture against the panels and does more harm than no cover at all.
A well-ventilated, emptied caravan with no soft furnishings in it will get through a winter without mould in most cases, with no power at all.
If you do have mains power in storage
Some storage sites and most home driveways do allow a supply. If yours does, the aim is gentle background warmth that keeps surfaces above the dew point, not comfort heating.
The right device is a thermostatically controlled heater set to its lowest useful level, so it cycles on only when the temperature drops. The Ceramic Heater MKK-230 has a 500W setting and an adjustable thermostat, which is the correct shape of tool for this. Set at a low target it will run for a small fraction of the time.
Before you do it, check all of the following:
- The storage site permits unattended appliances in writing. Many explicitly do not, and doing it anyway may void both their liability and your insurance.
- Your insurance policy permits it. Check the wording rather than assuming.
- The heater stands on a hard, level, non-combustible surface with clear space around the intake and the outlet.
- Nothing can fall onto it or against it. Secure it so it cannot move if the van is knocked or moved.
- It is plugged directly into a socket, not into a coiled extension reel.
- There is a working smoke alarm in the van.
- Somebody checks the van periodically.
If any of those cannot be satisfied, do not do it. Ventilation and moisture traps are the safer answer and they work.
What about a dehumidifier instead?
A dehumidifier removes moisture from the air rather than warming surfaces, which is a direct attack on the problem. Two practical caveats apply in a caravan.
First, compressor dehumidifiers work poorly at low temperatures, which is exactly when you need them. Desiccant types cope better in the cold. Second, a dehumidifier needs emptying or draining, and in an unattended van a full tank means it simply stops.
For most stored caravans, passive moisture traps combined with good ventilation are the more practical option, precisely because nothing needs power or attention.
Keep the battery alive instead
If you are going to use the electricity for anything in storage, keeping the leisure battery charged is a better use of it than heating. A flat lead-acid battery sulphates over a winter and may never recover, and replacing it costs considerably more than the electricity would have.
Either remove the battery and keep it on a maintenance charge at home, or leave it connected to a solar panel and controller. The maintenance load is small enough that even weak December sun can cover it.
The recommendation
- Drain the water system completely. This removes the frost risk entirely.
- Empty the van of everything soft and open every door, locker and vent.
- Fit a breathable cover and put moisture traps in.
- Deal with the battery, by removal or by solar.
- Only if the site and your insurer both permit it, add a thermostatic heater on its lowest setting as a belt-and-braces measure.
Steps one to four solve the problem. Step five is optional, and it is the only one with a risk attached.