Dehumidifier or Hygrometer: What Actually Helps Against a Damp Home?

Measure first, then buy

Many people buy a dehumidifier the moment their windows run wet. Often that isn’t necessary: wet windows in the morning can simply mean a lot of moisture builds up overnight and the room is aired too late. A hygrometer shows you what’s really going on.

How to measure usefully:

• Compare several rooms: bedroom, bathroom and living room behave very differently.
• Read at fixed times: after getting up, after showering, in the evening.
• Note it for a few days: only then can you see whether readings are briefly or permanently high.

How to read the numbers

Humidity	Meaning	What to do
below 35 %	rather dry	air for shorter periods, see Dry air from heating
40–60 %	good	carry on
60–65 % briefly	normal after showering or cooking	air the room straight away
above 60 % for long periods	too damp, mould risk	adjust airing and heating, then dehumidifier

Short peaks are normal. If the bathroom jumps to 80 % after a shower and is back to 55 % half an hour later, all is well. It becomes a problem when readings stay high for hours or days.

Step 1: Get airing and heating right

Before you spend money on a machine, try this consistently for a week:

1. Air rooms fully 3–4 times a day, windows wide open, about 5 minutes in winter. More in How to ventilate and heat in winter.
2. Heat all rooms moderately, and don’t let the bedroom drop much below 16 °C.
3. Reduce moisture sources: lids on pans, extractor fan on, no laundry drying in the bedroom.
4. Wipe condensation away each morning, see Condensation on windows.

If readings settle around 50 %, you don’t need a dehumidifier.

Step 2: When a dehumidifier makes sense

An electric dehumidifier is worthwhile if:

• you regularly dry laundry indoors,
• you live on the ground floor or in a basement flat, or next to cold external walls,
• after a leak, or in a new build whose walls are still drying out,
• humidity stays above 60 % despite good airing.

Compressor or desiccant? For normally heated rooms a compressor unit is the usual choice. In cold spaces like an unheated cellar, desiccant units work better.

Choose the right size: The litres-per-day figure is usually measured at 30 °C and 80 % humidity, i.e. lab conditions. In a home at 20 °C a unit removes much less. Better one size too big than too small.

Placement: in the middle of the room, away from walls and curtains, with doors and windows closed. Set the humidistat to about 50–55 %.

What about moisture-absorber tubs?

Tubs with calcium chloride or granules hold only a few hundred millilitres of water a week, depending on size. A household releases several litres of moisture into the air every day. They’re fine for a wardrobe, a camper or a guest bathroom, but they won’t noticeably dry out a damp home.

Already found mould?

You can remove small patches on smooth surfaces yourself, for example in the shower, see Remove mould in the shower. But fix the cause, or it will come back. For large areas, mould in wallpaper or plaster, or recurring growth, get a professional to find the cause.