The fastest way to lower humidity is to remove moisture at the source
The most direct method is to run a dehumidifier—a machine that pulls water vapor from the air and collects it in a tank or drains it continuously. But dehumidifiers work best when you also stop moisture from entering the room in the first place. That means fixing leaks, venting bathroom and kitchen exhaust fans outside (not into the attic), and running your air conditioner, which removes humidity as a side effect of cooling.
If you do not have a dehumidifier yet, you can lower humidity when ready by opening windows on dry days, running exhaust fans, and wiping down wet surfaces. These are temporary fixes, but they work while you decide whether to buy a machine or call a professional.
Key Takeaways
- A dehumidifier removes moisture from air by pulling it through cold coils and collecting water in a tank or drain line.
- Bathroom and kitchen exhaust fans must vent outside the house, not into the attic or crawlspace, or they will make humidity worse.
- Air conditioners remove humidity as they cool, so running one is often enough in summer without a separate dehumidifier.
- Humidity above 60 percent creates conditions for mold and dust mites; below 30 percent can crack wood and irritate skin.
- The size of the dehumidifier matters—a machine rated for 1,500 square feet will not work in a 3,000 square foot basement.
How a dehumidifier removes water from the air
A dehumidifier works by pulling humid air across cold coils (similar to the coils in a refrigerator). When warm, moist air hits those cold coils, the moisture condenses into liquid water, the same way water beads on a cold window. That water drips into a collection tank or a drain line, and the dried-out air is pushed back into the room.
The machine keeps running until the air in the room reaches the humidity level you set—usually between 40 and 60 percent relative humidity. Once it hits that target, the dehumidifier cycles on and off to maintain it. If the tank fills up, most machines have a float switch that shuts them off automatically so they do not overflow.
Dehumidifiers are most effective in enclosed spaces where air can circulate through the machine repeatedly. A basement with the door closed works better than a basement with doors open to the rest of the house, because the machine does not have to dry out the entire house.
Fixing the sources of moisture before running a dehumidifier
A dehumidifier will lower humidity, but it cannot fix the reason humidity is high in the first place. If water is leaking into the room, or if exhaust fans are venting moisture indoors instead of outside, the dehumidifier will run constantly and use a lot of electricity without solving the problem.
Check for these common sources: bathroom exhaust fans that vent into the attic instead of through the roof, kitchen range hoods that do not have outdoor ducts, dryer vents that terminate indoors, and foundation leaks or groundwater seeping into basements. Each of these adds moisture faster than a dehumidifier can remove it. If you find a leak, have it repaired before you buy a dehumidifier. If you find an exhaust fan venting indoors, have a contractor reroute it outside.
In basements, also check the grading around the foundation—water should slope away from the house, not toward it. If the ground slopes toward your foundation, water will seep in during rain, and no dehumidifier will keep up.
Using air conditioning to reduce humidity without a separate machine
An air conditioner removes humidity as it cools. When you run your AC, the indoor coils work the same way a dehumidifier's coils do—they condense moisture out of the air. That water drains outside through the condensate line, and the room gets both cooler and drier.
In summer, running your air conditioner may be enough to keep humidity below 60 percent without buying a dehumidifier. The catch is that AC only removes humidity while it is cooling—once the room reaches your set temperature, the compressor shuts off and humidity starts climbing again. In humid climates or in rooms that do not cool well, you may still need a dehumidifier to run alongside the AC.
If you have a central air system, make sure the condensate drain line is clear and draining outside. A clogged drain line can cause water to back up into the attic or crawlspace, creating mold and rot.
Sizing a dehumidifier to match your room or space
Dehumidifiers are rated by how many pints of water they can remove per day. A small bedroom might need a 30-pint machine, while a large basement could need 70 pints or more. If you buy a machine that is too small, it will run constantly and never catch up. If you buy one that is too large, you will waste money and electricity.
The size you need depends on the room's square footage, how wet it is, and how well it is sealed. A basement with active water seepage needs a larger machine than a dry basement. A room with poor ventilation needs a larger machine than one with good air circulation. Most manufacturers provide a sizing chart based on square footage and humidity level—check the manual or the product page before you buy.
Also consider where the water will go. Some dehumidifiers have a tank you empty by hand, which works for small rooms but becomes tedious in larger spaces. Others have a drain hose that runs to a floor drain or sump pump, which is more convenient for basements and crawlspaces.
Temporary ways to lower humidity without a dehumidifier
If you do not have a dehumidifier yet, you can lower humidity by opening windows on dry days, running exhaust fans, and wiping down condensation. These methods work best in spring and fall when outdoor humidity is lower than indoor humidity.
Run bathroom and kitchen exhaust fans during and for 20 minutes after showers and cooking. Make sure they vent outside, not into the attic. In basements, open windows on days when the outdoor humidity is lower than the indoor humidity—check a weather app to see the outdoor dew point before you open them. Close windows as soon as the outdoor air becomes more humid than the indoor air, or you will make the problem worse.
Wipe down windows, pipes, and walls where water is condensing. This does not remove humidity from the air, but it prevents mold from growing on wet surfaces. Also run a fan to keep air moving—stagnant air allows moisture to collect in corners and on cold surfaces.
What humidity level is healthy and how to measure it
The ideal indoor humidity is between 40 and 60 percent relative humidity. Below 30 percent, wood floors and furniture can crack, and your skin and sinuses become irritated. Above 60 percent, mold and dust mites thrive, and you may see condensation on windows and pipes.
You can measure humidity with an inexpensive hygrometer, a small device that costs $10 to $30 and displays the current humidity level. Digital hygrometers are more accurate than dial types. Place it in the room you want to monitor, away from direct sunlight and heat sources, and check it daily for a week to see how humidity changes.
If humidity stays above 60 percent even with windows open and fans running, you need either a dehumidifier or to fix a moisture source. If it stays below 30 percent, you may need to add moisture instead—a humidifier or straightforward running a shower can help.
When to call a professional instead of buying a dehumidifier
If humidity is high because of a leak, poor ventilation, or grading problems, a dehumidifier will only mask the problem. You will run it constantly, pay high electricity bills, and the underlying issue will get worse. Call a contractor if you see water stains on walls or ceilings, mold growth, or water pooling in the basement after rain.
A professional can identify whether the problem is a roof leak, foundation crack, clogged gutter, poor grading, or missing exhaust venting. Some of these are straightforward fixes—rerouting a dryer vent costs $200 to $400. Others, like fixing foundation cracks or regrading the yard, are more expensive but necessary to prevent structural damage.
If you are not sure whether the problem is fixable or just annoying, start with a dehumidifier while you save for repairs. But do not assume a dehumidifier is a permanent solution to water intrusion.
Frequently Asked Questions
Can I use a dehumidifier in a room with the door open to the rest of the house?
You can, but it will be much less effective. The dehumidifier will have to dry out the entire connected space, not just the one room, so it will run longer and use more electricity. Close the door to the room you want to dehumidify, and the machine will work faster and use less power.
Where should I place a dehumidifier in a room?
Place it away from walls and furniture so air can flow freely around it. The intake (usually the back or side) should have at least 12 inches of clearance. Avoid placing it in corners or against windows, where air circulation is poor. In basements, place it near the dampest area but not directly against a wet wall.
Do I need to empty the tank every day?
It depends on the humidity level and the machine's capacity. A small dehumidifier in a very humid room may fill a 2-gallon tank in a few hours. A larger machine in a moderately humid room might fill it once a day or less. If you do not want to empty it manually, buy a model with a continuous drain hose that runs to a floor drain or sump pump.
Will a dehumidifier help with mold that is already growing?
A dehumidifier will slow mold growth by keeping humidity below 60 percent, but it will not kill existing mold. You need to clean mold with a brush and a diluted bleach solution (or a commercial mold cleaner), then keep humidity low to prevent it from coming back. If mold covers more than 10 square feet, call a professional.
Can I use a dehumidifier in a cold basement?
Yes, but it will be less efficient. Dehumidifiers work best when the air temperature is above 65 degrees Fahrenheit. In cold basements, the coils may frost over, and the machine will shut down. If your basement is cold and damp, insulate the walls and run a small heater alongside the dehumidifier, or use a low-temperature dehumidifier designed for cold spaces.