Comparison
Electric dehumidifier vs moisture traps and crystals
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In short
Moisture traps and crystals absorb a small amount of water slowly, which suits a cupboard, wardrobe or car. An electric dehumidifier removes litres of water a day from a whole room or home. If your windows stream or walls are damp, traps will not keep up; an electric dehumidifier will. Use traps only for small, enclosed spaces.
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Our verdict
Use moisture traps and crystals for wardrobes, cupboards, cars and stored caravans. Buy an electric dehumidifier for any room with condensation, damp smells or slow-drying washing, because only a machine removes enough water to make a difference.
Moisture traps, damp crystals and dehumidifier bags are cheap, silent and need no plug, so they are often the first thing people try. They do work, but on a tiny scale. A tub of calcium chloride crystals draws water from the air slowly and turns it into a brine. An electric dehumidifier draws air through a machine and removes far more water every hour. This guide compares the two honestly, explains where each has a place, and shows how to tell when a room needs more than a tub on the windowsill.
How moisture traps work
Most traps use calcium chloride crystals. The crystals are hygroscopic, meaning they absorb water vapour from the air, and as they do so they dissolve into a liquid that collects in the lower chamber. When the crystals are used up, you replace the refill. Some products use silica gel bags instead, which can often be dried out in an oven or microwave and reused, following the maker's instructions.
Traps rely on air reaching them by natural movement. There is no fan, so they work best in small, still, enclosed spaces where the air volume is low.
How an electric dehumidifier works
An electric dehumidifier uses a fan to pull room air through the machine. A compressor unit condenses water on a cold coil; a desiccant unit absorbs it on a wheel and releases it with heat. Either way, the water drains into a tank or down a hose. Machines are rated in litres a day; for example, the Bosch Dry 1000 is listed at 10 litres a day and the EcoAir DD3 Slimline at 10 litres a day.
Those ratings are at test conditions, and real extraction in a UK home is lower. Even so, a machine removes vastly more water than a trap of any size. See our litres a day ratings explainer.
Scale: grams against litres
A single family can add several litres of moisture to the air every day from breathing, cooking, showers and drying washing. A trap simply cannot keep pace with that. A machine can, and with a humidistat it holds the room at a target rather than just soaking up what it can.
| Moisture trap or crystals | Electric dehumidifier | |
|---|---|---|
| Typical scale | Small amounts over days or weeks | Litres a day |
| Power | None | About 150 to 660 W by type |
| Noise | Silent | Some fan noise |
| Best space | Wardrobe, cupboard, car, caravan in storage | Rooms and whole homes |
| Ongoing need | Refills | Electricity, filter cleaning |
| Controls humidity to a target | No | Yes, with a humidistat |
Where traps make sense
Place traps on a level surface away from children and pets, because the liquid brine can damage surfaces and should not be touched or swallowed. Empty and replace them as the maker advises.
- Inside a wardrobe against a cold outside wall
- Under a sink or in a cupboard with a musty smell
- In a car with misting windows
- In a caravan or boat in storage, where there is no power
- In a small, closed space alongside a dehumidifier in the main room
Note:Calcium chloride brine can mark wood, metal and fabrics. Keep traps upright and on a protected surface, and follow the label for disposal.
Where you need a dehumidifier
If windows are wet every morning, there is black mould in corners, or washing takes days to dry, the room has more moisture than any trap can handle. A dehumidifier with a humidistat set to around 50 to 60 % RH will bring it down and hold it there. Choose a compressor model for heated rooms and a desiccant model for cold ones.
Persistent damp in walls, especially low down or around windows and roofs, may be a building problem rather than everyday condensation. Our guide on how to treat damp walls explains the difference; if it persists, speak to your landlord or a qualified surveyor.
Running a dehumidifier sensibly
The usual worry about switching from traps to a machine is the electricity. A dehumidifier with a humidistat only runs until the room reaches its target, then cycles on and off, so it rarely runs flat out all day. A compact compressor model such as the Bosch Dry 1000 is listed at 175 W. Multiply watts by hours and divide by 1,000 for kWh, or try the running-cost calculator.
Set a target of around 50 to 60 % RH, keep doors to the treated room closed, and clean the filter regularly. Our guide on how long to run a dehumidifier gives typical hours by season.
Frequently asked questions
Do moisture traps actually work? Yes, on a small scale. They suit cupboards, wardrobes and cars, but cannot keep up with the moisture in a lived-in room.
Are dehumidifier crystals as good as an electric dehumidifier? No. Crystals absorb small amounts slowly, while an electric unit removes litres a day and can hold a room at a set humidity.
Can I use both together? Yes. Many homes run a dehumidifier in the main living space and keep a trap or two in wardrobes and cupboards.
What you need
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Meaco Arete Two 20L: 38 dB and H13 HEPA filter
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Pro Breeze 30L/day: humidity sensor and drain hose