Cabin dehumidifiers address one of the most consequential issues with long-term storage of any classic car, the condensation, mildew, and moisture-related damage that develops inside the cabin when the car is left static for extended periods. Condensation cycling between warm and cool temperatures causes moisture to accumulate inside the cabin, the moisture encourages mildew growth on upholstery and carpets, and the damp conditions accelerate corrosion of exposed metal surfaces, while the resulting musty cabin smell is difficult to eliminate once established. A cabin dehumidifier eliminates the moisture before it can cause these problems.
How Cabin Dehumidifiers Work
Cabin dehumidifiers use silica gel, calcium chloride crystals, or other hygroscopic materials to absorb moisture from the cabin air, placed inside the cabin during the storage period, typically on the floor of the passenger footwell or on a rear shelf, where they draw moisture from the surrounding air through normal diffusion. Over the storage period the dehumidifier accumulates the moisture that would otherwise condense onto cabin surfaces, keeping the air inside the cabin dry, with the accumulated moisture collected inside the container and no leakage onto the surrounding interior. The unit requires no external power supply and no maintenance during its working life, only periodic renewal when the absorbent material has reached its full capacity, with quality units using a colour-change indicator, blue or pink crystals showing fresh material and the changed colour showing saturated material that needs renewal or recharging.
Rechargeable & Disposable Types
Rechargeable dehumidifiers use silica gel crystals that absorb moisture from the air and are then dried out periodically, either by plugging the unit into an electrical socket for several hours or by heating the absorbent material in a domestic oven or microwave to drive out the absorbed moisture, after which the unit is ready for reuse, making them economical for long-term use as they require no consumable materials. Disposable dehumidifiers use calcium chloride granules in a container with a collection tray beneath, the granules absorbing moisture and dissolving into a liquid that collects in the tray, effective but needing replacing once the granules have fully dissolved. For maximum protection a dehumidifier should be placed in the cockpit and another in the boot, as both areas are susceptible to condensation damage, and on the mid-engined MGF and TF the cabin sits between the front luggage compartment and the rear engine bay, both of which can harbour moisture.
Storage Best Practice
Cabin dehumidifiers are one element of good storage practice for any classic MG, the other elements being keeping the car covered with a breathable cover, ensuring the cabin is dry before storage begins, as any rain ingress left to dry inside the cabin will overload even a quality dehumidifier, and leaving the cabin slightly ventilated rather than completely sealed, so the dehumidifier can draw fresh moisture rather than saturating local pockets of high-humidity air. For larger or more damp spaces an electric plug-in dehumidifier running in the garage provides continuous active moisture removal, protecting not only the car but the tools and other items stored alongside it, which is particularly relevant for the timber-framed bodies of the early T-types, where controlling storage humidity protects both the steel panels and the ash sub-structure from damp damage. With a dehumidifier in place and proper storage practice, the cabin emerges from even a long lay-up in the same condition it went into it, the upholstery free of mildew, the carpets dry, and the exposed metalwork free of the corrosion that damp storage would otherwise have caused.