Last Updated on October 24, 2026 by Umar Farooq
How to lower humidity in house, in order: stop water getting in, get the damp air out, and only then buy a machine to mop up what is left. Most people start at step three, which is how you end up emptying a bucket every day for a house that has a leak.
I think of it as a bath with the tap running. You can bail faster, or you can turn the tap off first. The rest of this is about finding the tap.
How to lower humidity in house: take a week of readings first
A house does not have one humidity. It has one per room, and they disagree, so the first job is to find out which ones are high and when.
Put a cheap hygrometer in three places: the bedroom, the room you cook in, and the coldest or lowest spot you own (cellar, utility room, north-facing back room). Note the readings morning and evening for a week. The target is the one the EPA gives: keep indoor humidity below 60%, ideally between 30% and 50%. If you want the reasoning behind that band, what indoor humidity should be walks through it.
Then read the pattern, because the pattern points at the cause:
| What the readings do | What it usually points to | Start here |
|---|---|---|
| High everywhere, all week | A whole-house moisture load, or a very humid climate | The sources and exits below, then a machine |
| High in one room only | A local source: bathroom, airer, a leak | That room, not the house |
| Highest at the bottom of the house | Moisture rising from the ground | Soil, drainage, the crawl space |
| Spikes after showers and cooking, then falls | Steam with nowhere to go | Extractor fans and lids |
| Rises on wet days, falls on dry ones | Damp outdoor air getting in | Ventilation timing |
That table is my own reading of how these things behave, not a published diagnostic. Treat it as a way to decide where to look first.
Six routes water takes into a house
Every litre of water vapour in your air arrived from somewhere: people, cooking, showers, laundry on airers, leaks and the ground. The diagram shows the usual routes in, and the three exits that cost nothing.
Here is the one opinion I will push on this page: do not buy a dehumidifier until you have looked for the source. A machine in a house with a live leak is a bucket under a dripping tap. The EPA’s moisture guidance makes the same point about the whole job: keep humidity low, and when water leaks or spills occur, act quickly.
Fix the water that should not be there
Do this before the steam and the fans, because it does not matter how well you ventilate if the roof is feeding the loft.
- Walk the house after heavy rain. Look for stains on ceilings, a damp patch where a wall meets the floor, and gutters overflowing against brickwork.
- Check under every sink and behind the washing machine. A slow weep produces no puddle, only a permanently damp cupboard.
- Look at the ground outside. The EPA’s advice is to make sure the ground slopes away from the foundation, so rainwater runs off instead of soaking in beside the wall.
A leak that has been going for months leaves materials wet long after it is fixed. Expect the air to take days to settle and the structure weeks.
Cover bare soil: the crawl space is a wet room nobody visits
If you have an exposed dirt floor under the house, in a crawl space or a cellar, it is putting vapour into the building continuously. The US Department of Energy’s weatherization job aid says it plainly: exposed dirt floors allow ground vapour and soil gases to enter when a vapour retarder is missing or not working.
Its specification is concrete: a ground cover of at least 6 mil (0.15 mm) with a permeance of 0.1 perm or less, running at least 6 inches (15 cm) up the walls and piers, with seams overlapped by at least 12 inches (30 cm). That is a job a competent DIYer can do over a weekend, provided the space is dry and clear of debris.
It is a ground-vapour fix, not a drainage fix. If liquid water is coming in, the plastic hides the symptom, so sort the drainage first.
Vent the steam where it starts
Showers, cooking and drying clothes put the most water into the air in the shortest time, so catch it at the source rather than in the next room.
- Ducted extractors that go outside. One that ends in the loft just relocates the damp to the roof timbers. Check where yours terminates.
- Run it after you finish. My rule of thumb is 15 to 20 minutes after a shower, not until the light goes off. That is my own habit, not a measured standard.
- Cooker hood on, lids on. An open pan is a small steam machine.
- Dryers vented outside. The EPA lists clothes dryers and stoves among appliances to vent to the outside where possible.
- Shut the bathroom door during the shower. An open door sends the steam on a tour of the house.
Laundry dried on airers deserves its own plan. Drying clothes indoors without mould covers it.
Open the windows only when the outside air is the drier
Ventilation lowers humidity when the air outside holds less water than the air inside, and raises it when it does not. Cold, clear days usually win, because cold air carries little moisture and warms up dry. A warm, muggy afternoon loses.
Ten to twenty minutes with windows open on two sides beats one window left ajar all day. If the outside air is damp more often than not where you live, ventilation is no longer your drying tool, and that is the point to look at mechanical options.
Let the air conditioner do part of the job
A cooling coil pulls water out of the air for the same reason a cold glass sweats: the surface is below the air’s dew point. If you have central air, running it with clean filters and coils is a form of dehumidification you already own.
The catch is that a system sized too big cools the house quickly and shuts off before it has dried much. If summer rooms feel cool and clammy, that is the usual reason, and it is the point where a separate dehumidifier starts to earn its place.
When a machine is the right answer for a whole house
Buy one when readings stay above 60% for weeks after the sources and exits are sorted. For a single floor, a portable unit on the landing with the internal doors open treats several rooms at once; where to put a dehumidifier explains why. To pick the capacity, the sizing guide takes it from there.
For the whole building, ENERGY STAR says whole-home units suit humid climates and fairly airtight homes with central air, installed on the ducting and drained to a floor drain or pump by a professional, and that the optimum range is 30% to 50%. That is the point to pay an installer rather than buy a portable and hope.
Lower humidity in the house by working down the list, never up it
The order is the whole advice: read the house, fix the water, cover the ground, vent the steam, ventilate on the right days, and let a machine take what remains. Skip to the last step and you will be buying capacity to fight a problem a roll of polythene or a fan duct would have solved.
If you have already bought the machine, fair enough. Run it, and do the other steps anyway; it will thank you by running less.
FAQ
How can I lower humidity in my house quickly?
Run the extractor fans, shut the bathroom and kitchen doors while they work, and open windows on two sides for 15 to 20 minutes if the air outside is drier than the air inside. That drops the reading within hours. A portable dehumidifier is the fastest option when the weather is damp.
How do I lower humidity in my house without a dehumidifier?
Cut the sources first: lids on pans, dryers vented outside, clothes dried outdoors, leaks fixed. Then remove steam through ducted fans and ventilate when outdoor air is drier. Cover any bare soil under the house. This is enough in many homes, and it is the order that stops the problem returning.
Why is my house so humid?
Usually because moisture is being added faster than it leaves: cooking, showers, laundry drying indoors, a leak, or damp ground. A week of hygrometer readings in different rooms shows which. Poor extraction and damp outdoor air making it inside are the common amplifiers.
Does an air conditioner lower humidity in a house?
Yes. The cold coil condenses water from the air passing over it, which is the same principle a dehumidifier uses. It works best when the system is correctly sized and the filters and coils are clean, and less well when an oversized unit shuts off too soon.
What humidity should a house be?
Below 60%, and ideally between 30% and 50%, according to the EPA. In cold weather the number often needs to sit toward the lower end to keep windows from running wet.
