How to Lower Humidity in Your House

This page carries no product picks. There is nothing on it we can sell you, which is exactly why it is worth reading before the pages that do.

1. Stop making so much moisture (biggest single win)

A household generates a surprising amount of water vapor, and most of it comes from a handful of activities:

• Showers and baths. Run the extractor fan during and for 15-20 minutes after, with the door closed. A fan that vents into a loft rather than outside is moving the problem, not solving it - check where the duct goes.
• Cooking. Lids on pans, and the hood on. Boiling an uncovered pan for 20 minutes puts a substantial amount of water into the air.
• Tumble dryers. A vented dryer must vent outdoors. A condenser dryer must have its reservoir emptied. Either one venting into the room is adding liters of water per load.
• Drying laundry indoors. A single load of wet washing carries around two liters of water, and all of it ends up in the air of whatever room it dries in.
• Unvented gas heaters. Burning gas produces water vapor as a combustion product.

2. Ventilate - but check the outdoor air first

Opening windows works when the outdoor air holds less moisture than the indoor air. In cool dry weather it is the fastest dehumidifier you own and it costs nothing.

In warm humid weather it does the reverse, which is why airing out a basement in August often makes it worse: warm humid outdoor air meets cool basement surfaces and condenses on them. The number to check is the outdoor dew point, not the relative humidity or the temperature - if the outdoor dew point is below your indoor surface temperatures, ventilating helps.

3. Warm the cold surfaces

Condensation forms where warm moist air meets a surface colder than its dew point. That is why it appears on windows, on external walls behind furniture, and in unheated corners first.

• Pull furniture a few inches off external walls so air can move behind it
• Leave closet and wardrobe doors ajar on external walls
• Heat rooms a little rather than leaving some completely unheated
• Insulate cold water pipes that sweat in summer

4. Stop drying laundry indoors

It deserves its own heading because it is the single largest avoidable moisture source in many homes, and because it is so easy to overlook - the water has to go somewhere, and in a closed house that somewhere is the walls.

5. Find the leaks

Slow leaks under sinks, at washing machine connections, at toilet bases and on waste traps are common and easily missed. Dry paper towel taped under each joint overnight is a quick survey. Outside, check that downpipes discharge away from the foundation and that the ground slopes away from the house - groundwater is the most common basement moisture source and it does not respond to appliances at all.

6. Then, if it is still above 60%, dehumidify

Having done all of the above, a persistent reading above the EPA’s 60% ceiling in a basement or a specific room is a genuine case for a dehumidifier - which is when sizing it correctly starts to matter.

What does not work

• Houseplants. They release water vapor. They raise humidity, not lower it.
• Bowls of salt or rice. Absorbs a trivial amount and stops when saturated.
• Air purifiers. They filter particles. They have no effect on humidity whatsoever - which device do I need covers why this confusion is so common.
• Heating alone. Warming a room lowers relative humidity by raising the air’s capacity, but the same amount of water is still there and it will condense as soon as the room cools. Useful alongside ventilation, useless without it.