Use a dehumidifier when indoor humidity stays above 50 percent and you notice moisture damage, mold, or musty smells

A dehumidifier works best as a response to a specific problem, not as background equipment. The right time to run one is when your home's humidity level climbs above 50 percent and you see or smell the results: condensation on windows, soft spots in drywall, visible mold, or that damp basement odor. You can measure humidity with an inexpensive hygrometer (a small digital meter that costs $10 to $30), which tells you whether you actually have a moisture problem or just think you do.

The Environmental Protection Agency recommends keeping indoor humidity between 30 and 50 percent. Below 30 percent causes dry skin and respiratory irritation; above 50 percent feeds mold and dust mites. If your hygrometer reads 55 percent on a normal day, a dehumidifier will help. If it reads 75 percent, you have a ventilation or water intrusion problem that a dehumidifier alone cannot fix — you need to find the source first.

Key Takeaways

  • Buy a hygrometer before you buy a dehumidifier so you know whether humidity is actually the problem.
  • Run a dehumidifier when indoor humidity stays above 50 percent for more than a few days, especially in basements, bathrooms, and laundry rooms.
  • A dehumidifier is a temporary fix for moisture; if humidity stays high even with one running, you have a leak, poor ventilation, or drainage problem that needs repair.
  • Dehumidifiers cost $0.50 to $2.00 per day to run, depending on size and your local electricity rates, so using one only when needed saves money.
  • Seasonal use — spring and summer in humid climates, or year-round in basements — is more common than running one constantly.

Basements and crawl spaces almost always need dehumidification

Basements stay damp because they are below ground level and surrounded by soil that holds moisture. Even in dry climates, a basement's temperature stays cool, and cool air cannot hold as much moisture as warm air, so humidity rises. If your basement hygrometer reads above 60 percent, a dehumidifier will prevent mold on stored items, protect wooden joists and subflooring, and stop that earthy smell.

Crawl spaces are worse than basements because they have no floor to block ground moisture. If your crawl space has a dirt floor, a dehumidifier alone will not solve the problem — you need a vapor barrier (plastic sheeting) laid over the soil first. Once the barrier is in place, a dehumidifier keeps humidity from climbing back up. Without the barrier, you are just running the machine to no real effect.

Bathrooms and laundry rooms need dehumidification after showers and washing

These rooms generate moisture spikes: a 20-minute shower can push bathroom humidity to 80 or 90 percent. A dehumidifier in the bathroom works, but a better first step is a working exhaust fan that vents to the outside (not into the attic). If your exhaust fan is broken or missing, or if you have a bathroom with no fan, a dehumidifier will catch some of the moisture and prevent mold on the ceiling and walls.

Laundry rooms have the same issue. A clothes dryer that vents to the outside removes most moisture, but if your dryer vents indoors or the vent is clogged, humidity climbs fast. Run a dehumidifier in the laundry room on wash days, or fix the dryer vent first and see whether you still need one.

Kitchens rarely need a dehumidifier if your range hood works

Cooking and boiling water release steam, but a range hood that vents outside handles most of it. If your range hood is missing, broken, or vents into the kitchen instead of outside, humidity can climb during and after cooking. A dehumidifier will help, but installing or fixing the hood is the real solution.

If you rent and cannot install a hood, a portable dehumidifier in the kitchen during cooking season (winter, when you use the oven more) is a practical workaround. Run it while you cook and for an hour after, then turn it off.

Seasonal humidity spikes call for temporary dehumidifier use

In humid climates, spring and summer bring outdoor moisture indoors through open windows and doors. If your hygrometer reads 55 to 65 percent on humid days but drops below 50 percent on dry days, you have a seasonal problem. Run a dehumidifier during the humid months and store it when the weather dries out.

In dry climates, humidity rarely climbs above 40 percent, so a dehumidifier is usually unnecessary. In temperate climates, you might need one only in the basement year-round and in living spaces during summer. Check your hygrometer in each season to know when to pull the machine out.

Stop using a dehumidifier if humidity stays high despite running it

If you run a dehumidifier for a week and humidity is still above 60 percent, the machine is not the problem — something else is feeding moisture into the room. Common causes are a roof leak, a burst pipe, poor grading that lets rainwater pool against the foundation, or a sump pump that is not working. A dehumidifier cannot outpace active water intrusion.

Before you buy a larger dehumidifier or run the current one 24/7, have a contractor inspect for leaks and drainage problems. Fixing the source costs more upfront but saves you money on electricity and prevents structural damage that a dehumidifier cannot stop.

Dehumidifier running costs and efficiency

A small dehumidifier (30 pints per day) uses about 300 to 700 watts and costs roughly $0.50 to $1.20 per day to run, depending on your local electricity rate. A large one (70 pints per day) uses 700 to 1,500 watts and costs $1.20 to $2.00 per day. Running one 8 hours a day for three months costs $40 to $180, depending on size and climate.

Energy Star dehumidifiers use about 15 percent less electricity than standard models for the same capacity. If you plan to run a dehumidifier for more than a few months a year, an Energy Star model pays for itself in lower bills over time. For seasonal or occasional use, a standard model is fine.

Frequently Asked Questions

Can I run a dehumidifier in every room at once?

You can, but it is expensive and usually unnecessary. Most homes need dehumidification only in basements, crawl spaces, and bathrooms. Run a dehumidifier where your hygrometer shows humidity above 50 percent, not in every room.

Should I close doors and windows when running a dehumidifier?

Yes. A dehumidifier works by pulling moisture out of the air in a closed space. If you open windows or doors, humid outdoor air replaces the dry air the machine just created, and the machine has to work twice as hard. Close the room and run the dehumidifier for at least a few hours before opening up again.

What humidity level should I aim for?

Keep indoor humidity between 30 and 50 percent. Below 30 percent causes dry skin and static electricity; above 50 percent promotes mold and dust mites. Most people feel comfortable around 40 to 45 percent. Use your hygrometer to find the level that works for your home.

Do I need a dehumidifier if I have air conditioning?

Air conditioning removes some moisture, but not always enough in very humid climates or in basements. If your hygrometer reads above 50 percent even with the AC running, a dehumidifier will help. In dry climates, AC alone is usually sufficient.

How often should I empty the dehumidifier tank?

That depends on humidity and the machine's capacity. A small dehumidifier in a very humid basement might need emptying every 8 to 12 hours; a large one in a moderately humid room might go 24 to 48 hours. Many dehumidifiers have a drain hose option so you can run a hose to a floor drain or sump pump and avoid emptying by hand.