Storage, humidity and dehumidification

On most classics, storage damage announces itself. On an E-Type, much of what matters is out of sight. The monocoque and the brazed tubular front frame are what decide whether a car is savable, and the areas that rot are the ones you cannot inspect without taking the bonnet off, which is a considerable operation. A car stored badly for three winters can look perfectly presentable while quietly deteriorating in the places that count. Controlling the air the car sits in is therefore not fastidiousness. It is the only practical alternative to inspection, and everything below follows from that.

The lay-up article covers preparing the car itself: fuel, tyres, the handbrake and the cover. This page covers the building around it. The winter driving article covers the other choice entirely. Between them, the three add up to the whole of the cold-weather question.

The target, and the disagreement between sources

Published recommendations for storage humidity cluster together but do not agree, and the honest way to present them is side by side. Auto Classica Storage and the Danish storage specialist Ole Dissing both give 40 to 60 percent relative humidity, on the basis that rust all but stops below 60 percent while leather, wood and rubber can dry and crack below 40 percent. CarCapsule gives a tighter 40 to 50 percent, citing corrosion research from the US National Institute of Standards and Technology. Cotes, a dehumidifier manufacturer, gives 35 to 55 percent. Munters, another manufacturer, gives 45 to 50 percent. Dantherm gives 55 to 60 percent at 18 to 20 degrees, though that is guidance aimed at professional storage facilities rather than a domestic garage.

The archive does not resolve this disagreement, because the sources themselves do not. What can be said is that nearly all of them overlap between 45 and 55 percent, and the E-Type adds a point of its own: the leather and timber in the cabin argue against running at the bottom of any range, so the middle of the band is the sensible target for this car.

Compressor against desiccant

Dehumidifiers for garages come in two types. A compressor or refrigerant unit condenses moisture out of the air over cold coils, exactly like a fridge in reverse. A desiccant unit passes the air over a rotating moisture-absorbing material and regenerates it with heat. The difference that matters in a British garage is cold. Compressor efficiency falls as the temperature drops, and here the sources disagree again: Motoring Research describes compressor units as ineffective below 15 degrees, Ole Dissing states that refrigerant units work down to 5 degrees and suit northern European conditions, and a third published account has them losing effectiveness below about 18 degrees and cutting out around 5. Desiccant units, by contrast, work down to near freezing, which is why they are so often recommended for unheated garages.

Two further points are worth knowing before choosing. A desiccant unit uses more electricity for the same extraction, though it returns warmth as well as dry air, since the regeneration heat ends up in the garage. A refrigerant unit, per Ole Dissing, returns roughly two and a half times its energy input as heat while it runs. Neither type is being recommended here; the right choice depends on how cold your garage actually gets in January, and a thermometer will tell you that better than any article can.

Heating is not the same answer

Warming a garage feels like it should solve the problem, and it helps, but it is not the same tool. Ole Dissing states that heating is around two and a half times less efficient than dehumidification as a way of lowering relative humidity, and that heating alone will not stop a cold car attracting condensation: the car's metal follows the temperature of the night rather than the day, so warm moist air in the garage still condenses on cold steel.

The E-Type sharpens this point. It is a car with a large bonnet and a considerable enclosed volume beneath it, around the engine, the frames and the inner wings, and that volume holds cold air long after the garage itself has warmed. The parts of the car that decide its future are also the parts slowest to follow the temperature of the room, which is the whole argument for removing the moisture from the air rather than trying to outrun it with heat.

The garage and the floor

The building sets the ceiling on what any machine can achieve. A brick or stone garage has thermal mass: it changes temperature slowly, which reduces condensation swings but also means the car lives at the average of the season. A steel-framed fabric shelter is the opposite case; it follows the weather closely, and condensation forming on the inside of the cover and dripping onto the car is a known failure of the type rather than a defect of one example.

The floor matters at least as much as the walls. A concrete slab over hardcore is a relatively dry base. A plastic sheet over grass or hardcore is better than bare earth but not sealed. Bare earth releases moisture continuously, day and night, winter and summer, and no dehumidifier sized for a garage will win that fight. A sealed vapour barrier between the ground and the air of the garage is the cheapest worthwhile improvement most owners can make, because it reduces what the machine has to remove rather than asking the machine to work harder. This is a statement of principle only; materials and methods belong to a builder, not to this archive.

Running it

No article can give you a running schedule from a table, because the right hours depend on your garage, your floor, your weather and your machine. Two inexpensive instruments answer the question directly. A hygrometer tells you the relative humidity the car is actually living in, and a humidistat, built into most dehumidifiers or available separately, switches the machine to hold a set level rather than running blindly. Set the humidistat in the middle of the band described above, watch the hygrometer for a few weeks through changing weather, and adjust from what it tells you. Anyone quoting fixed run hours or duty cycles without knowing your garage is guessing.

What to look for, by capability

• A humidistat, so the machine holds a target rather than running constantly or not at all.
• Automatic restart after a power cut, so a winter storm does not silently end your protection for a month.
• Continuous drainage, since a unit that stops when its tank is full is not protecting the car while you are away.
• Low temperature operation matched to how cold your garage genuinely gets, which is the compressor against desiccant question above.

No makes, models, prices or retailers are named, and none will be. The capabilities above are the specification; what meets it changes every year.

Pouches and crystals

Disposable or rechargeable moisture traps and silica gel pouches have a genuine role and a hard limit. Inside a closed cabin they will take moisture out of a small enclosed volume, which is useful for the seats, carpets and trim. They cannot dry a garage: the volume of air and the continuous moisture from the ground are orders of magnitude beyond what a pouch can hold. CarCapsule suggests swapping moisture traps roughly every sixty days from October to April in a humid climate, and notes that silica gel can be dried in a low oven and reused. Treat them as protection for the cabin and the boot, not as a substitute for controlling the air in the building.

The battery

A battery left connected will be flattened by the car's small standing drains and its own self-discharge, and a battery left flat through winter sulphates and never fully recovers. The two honest answers are to disconnect it, removing the earth lead so nothing can draw, or to leave it on a maintenance charger. A modern maintenance or conditioning charger is not the same thing as an old trickle charger: it monitors the battery and switches between charging and resting, where a trickle charger applies a small current continuously and can cook a battery over months. Charging any battery unattended calls for basic care: the charger in good order, the connections clean and tight, and nothing flammable against the battery. The battery locations and the awkward hold-down hardware differ between six-cylinder and V12 cars, and the charging system article covers both.

One piece of advice to treat sceptically

Some published sources suggest starting the engine and letting it idle periodically during storage. Treat this as contested rather than settled. The case against is straightforward: an engine that never reaches full operating temperature produces condensation in the exhaust and the crankcase rather than removing it, and each cold start adds fuel and water to the oil without the heat that would boil them off. The case for it rests on keeping oil films distributed and seals wetted, which is sincere. The archive does not resolve the dispute. Opinion is genuinely divided, and the only thing every source agrees on is that a proper drive, long enough to bring the engine fully up to temperature, does everything idling claims to do and more. If the car cannot be driven, the prepared lay-up described in the storage article is the safer course than the fortnightly cold start.

Common questions