The mould trick
Mould needs three things to grow: moisture, something to grow on, and time. Cut the moisture, kill the mould. Wiping walls with bleach feels productive but doesn't stop it coming back. A dehumidifier does.
What humidity level you want
Mould stops growing under 60% relative humidity. A healthy home sits between 40 and 55%. Anything over 65% and you're inviting trouble.
Buy a £10 hygrometer to spot-check. If your readings are over 60% most evenings, you've got a problem to solve.
How to size the unit
Dehumidifiers are rated in litres of water removed per day. Rough guide:
- Small room (bathroom, laundry): 6 to 8 L/day
- Medium bedroom: 10 to 12 L/day
- Living room or basement: 16 to 20 L/day
- Whole apartment: 25 L/day
Buy a notch bigger than you think you need. The unit runs less often, uses less energy, and lasts longer.
Compressor vs desiccant
Compressor: Standard, cheaper, struggles below 15°C. Best for most warm-climate homes.
Desiccant: Works at any temperature, including cold rooms. Good for unheated garages and basements, or anywhere genuinely cold. Uses a bit more electricity.
Where to put it
Centre of the room ideally, away from walls and curtains, with at least 15cm of clearance around the air intake. If you can see where the damp is coming from (a sweaty wall, the bathroom door), put the dehumidifier between that source and the rest of the room.
Quick wins while it's running
- Keep extractor fans on for 20 minutes after every shower
- Cook with the rangehood on, lids on the pots
- Don't dry clothes inside without ventilation
- Open windows for 10 minutes in the morning to flush overnight humidity
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