What humidity should I set my basement dehumidifier to?

Around 45 to 50% works well for most basements. The EPA recommends keeping indoor humidity below 60%, ideally 30 to 50%.

Why does my new 50-pint dehumidifier seem to do the same as my old 70-pint one?

Because the test changed in 2019: ratings are now measured at 65°F instead of 80°F, so the same capacity shows a smaller number. A new 50-pint unit is roughly comparable to an old 70-pint unit.

Should a basement dehumidifier run all the time?

In humid summers it may run a lot, which is normal. If it never shuts off and humidity stays high, it is undersized, the basement is very leaky to outside air, or water is coming in through walls or floor.

Can a dehumidifier stop a wet basement?

No. It dries the air, not water coming through walls or up through the floor. Fix the water source first, then use the dehumidifier to keep humidity in check.

Basement Dehumidifier Guide: Humidity Level & Size

What humidity should a basement have?

The U.S. EPA recommends keeping indoor relative humidity below 60%, ideally between 30% and 50%, to limit mold growth. Basements tend to sit above that range in summer: the walls and floor are cooled by the ground, and when warm, humid summer air touches them, its relative humidity rises and moisture condenses.

A cheap digital hygrometer (humidity meter) tells you where you stand. Put it in the middle of the basement, away from the dehumidifier, and check it over a few humid weeks. Readings that stay above 60% call for action.

Dehumidifier or waterproofing?

A dehumidifier removes moisture from the air. It is the right tool when the problem is humidity and condensation: musty smells, sweating walls or pipes, damp boxes, a clammy feel. It is not a fix for liquid water coming through walls or up through the floor – that water will keep coming no matter how hard the dehumidifier works, and the unit will run constantly. If you see puddles, wet floor edges or water at cracks, deal with the water first (see water in the basement after heavy rain), then use a dehumidifier to keep the air dry.

Not sure which you have? Tape a square of plastic sheet tightly to the wall for a day or two. Moisture on the room side means humid air (condensation); moisture on the wall side means water is coming through the wall.

Sizing: why the numbers changed in 2019

Dehumidifiers are rated in pints of water removed per day. In 2019 the U.S. Department of Energy changed the test conditions for portable dehumidifiers from 80°F to 65°F (at 60% humidity), to reflect conditions in a basement more realistically. Cooler air holds less water, so the same machine now shows a smaller number. According to ENERGY STAR, models that used to be sold as 30, 50 and 70 pints are now typically labeled around 20, 30 and 50 pints.

That matters when you read older advice or compare an old unit with a new one: a “50-pint” dehumidifier today is roughly what used to be called a 70-pint unit.

How big a dehumidifier do you need?

The Association of Home Appliance Manufacturers (AHAM) publishes a sizing table based on the area and how damp the space is. A version reproduced by the retailer Sylvane (based on the older 80°F ratings) looks like this:

Condition	1,000 sq ft	1,500 sq ft	2,000 sq ft
Moderately damp (musty in humid weather)	14 pints	18 pints	22 pints
Very damp (damp spots on walls and floor)	17 pints	22 pints	27 pints
Wet (walls sweat, some seepage)	20 pints	26 pints	32 pints
Extremely wet (wet floor, laundry, high load)	23 pints	30 pints	37 pints

Because basements are cooler than the old test conditions, sizing guides often recommend erring on the larger side. A unit that is slightly too big simply runs less; one that is too small runs all the time and still cannot keep up.

Portable, whole-house or crawl space unit?

Portable dehumidifiers are the standard choice for a single basement: inexpensive, easy to move and widely available. Most basements with a humidity problem start here.
Whole-house or ducted dehumidifiers are installed by an HVAC contractor and connected to ductwork or placed in the basement with their own ducts. They cost more up front but handle larger areas quietly and can drain continuously without a bucket.
Crawl space dehumidifiers are compact, rugged units designed to sit in a sealed crawl space and drain to a sump or outside. They are a common part of crawl space encapsulation.

Whichever type you choose, the target stays the same: humidity below 60%, ideally between 30% and 50%.

Setup tips

Use continuous drainage. Emptying a bucket every day gets old fast. Run a hose to a floor drain or the sump pit, or choose a model with a built-in pump that can lift water to a sink or out a window.
Set the humidistat around 45–50% and let the machine cycle. Going much lower wastes energy.
Close basement windows in humid weather. Opening them on summer days brings in more moisture, not less.
Give it airflow. Keep the unit a foot or so away from walls and furniture, and leave interior doors open so air can circulate.
Clean the filter regularly, and check the coils for frost if the basement is cool; many units have automatic defrost.
Look for ENERGY STAR. According to ENERGY STAR, certified dehumidifiers remove the same amount of moisture as comparable standard models while using less energy – meaningful for a machine that may run for months each year.

Reduce the moisture load first

A dehumidifier works best when there is less moisture to remove:

Vent the clothes dryer outside and keep the vent connection tight.
Insulate cold water pipes that sweat.
Fix gutters and downspouts and make sure the ground slopes away from the house.
Store items in plastic bins off the floor rather than in cardboard against the walls.
Seal a crawl space or bare-earth area connected to the basement – see is crawl space encapsulation worth it?

When to call a professional

The dehumidifier runs constantly but humidity stays above 60%.
You see liquid water, white efflorescence or damp floor edges – signs of seepage, not just humid air.
There is visible mold on wood, drywall or stored items.
You plan to finish the basement and want it dry first.

Our page on basement mold and humidity explains the options, from whole-house dehumidifiers to drainage systems.

Basement dehumidifier guide: what humidity level and what size?