Dehumidifier for Mold: Sizing, Settings and Cleaning

Yes, for prevention. Mold needs moisture. The EPA calls moisture the most important factor influencing mold growth indoors, and notes that mold does not need a lot of water to grow. Even a little condensation, in a bathroom or around a window sill, can be enough.

That is where a dehumidifier comes in. Among its actions to reduce humidity, the EPA lists using air conditioners and/or dehumidifiers when needed. Consumer Reports says a dehumidifier can bring the relative humidity inside your home to below 50 percent, and that above that level, dust mites, mildew and mold can grow. TDLR's consumer sheet gives the same advice: keep humidity no higher than 50% all day long, using an air conditioner or dehumidifier.

What a dehumidifier can't do

• It doesn't remove existing mold. The EPA says it is not enough to simply kill the mold. It must also be removed, because dead mold is still allergenic. A dehumidifier doesn't even kill it; it only stops new growth.
• It doesn't fix a leak. A dripping pipe, roof leak or wet slab keeps feeding mold no matter how dry the air is. The EPA's first step is to fix plumbing leaks and other water problems.
• It can't save soaked drywall or carpet. The EPA says porous materials such as ceiling tiles and carpet may have to be thrown away once they're moldy.

People search for "dehumidifier mold removal," but a dehumidifier is a drying tool, not a removal tool. Here is where it fits:

1. Before mold starts. Keep humidity in the 30 to 50 percent range so mold never gets a foothold.
2. Right after a leak or flood. The EPA says to dry water-damaged areas and items within 24-48 hours to prevent mold growth. Its water-damage table lists dehumidifiers for drying carpet, concrete, upholstery and wood, for example to reduce ambient humidity levels with dehumidifier when drying carpet.
3. After cleanup. Once a small patch is cleaned or a professional has removed the mold, the dehumidifier helps keep it from coming back.

If mold covers more than about 10 square feet, the EPA says to follow its professional remediation guidance rather than handle it as a homeowner; see the last section of this guide.

Table: target indoor humidity for mold prevention.

A setting of 45 to 50 percent sits inside every agency's range. The EPA says you can track humidity with an inexpensive meter. ENERGY STAR notes certified dehumidifiers have a built-in humidistat, and suggests a separate hygrometer if your unit doesn't display humidity.

Dehumidifiers are rated in pints of water removed per day. ENERGY STAR publishes a sizing chart for portable units, based on how damp the space is:

Table: ENERGY STAR recommended dehumidifier capacity range, pints per day. Source: ENERGY STAR.

ENERGY STAR's advice is that it's better to oversize than undersize. Consumer Reports groups units by room size instead: small units remove less than 30 pints of moisture per day for areas under 600 square feet, midsized units remove 30 to 40 pints of moisture per day for 600 to 800 square feet, and large units remove 40 pints or more.

A note on labels: Consumer Reports explains that the Department of Energy changed its test, lowering the test room temperature from 80° to 65° F, so units sold since 2020 typically claim 20, 30 or 45 pints per day. An older 50- or 70-pint unit isn't directly comparable to a new 30- or 45-pint one.

What to look for when buying

• ENERGY STAR certification. Certified models use 20% less energy than similar conventional units.
• A built-in humidistat so you can set 45 to 50 percent and let it cycle.
• A drain hose option or pump. Consumer Reports calls a pump the most hassle-free way to drain a dehumidifier. ENERGY STAR says some models accept a hose to a floor drain so you don't have to empty the bucket.
• Frost control if it will run in a cool space. Consumer Reports describes a sensor that shuts the unit off if frost forms on the coils.
• An easy-to-reach tank and filter, because you'll be cleaning them.

Where to put it

ENERGY STAR's placement tips: units with top air discharge can sit against a wall, others need space so air can circulate; keep doors and windows closed while it runs; and keep it away from dust, which can clog the coils.

Black mold in a dehumidifier is common, and it makes sense: the unit collects standing water all day. Consumer Reports warns that a dehumidifier that's not thoroughly cleaned can breed mold spores that are harmful to people with allergies.

You don't need to know what kind of mold it is. The CDC says you do not need to know the type of mold; remove it either way.

How to clean mold inside a dehumidifier:

1. Unplug it and empty the tank.
2. Gear up. For small cleanups, the EPA's minimum is gloves, an N-95 respirator, and goggles/eye protection. Do this outdoors or in a ventilated room.
3. Scrub the tank. The tank is hard plastic, a non-porous surface, so the EPA's method applies: scrub mold off hard surfaces with detergent and water, and dry completely. If you use bleach, the CDC says no more than 1 cup of household laundry bleach in 1 gallon of water, and rinse well. Check your owner's manual first, since some makers limit which cleaners you can use.
4. Clean the filter. Consumer Reports says to wash and dry the filter regularly, following your manual, to keep the unit efficient.
5. Dry everything before you put it back together.
6. Repeat on a schedule. Consumer Reports recommends deep cleaning and sanitizing the emptied tank at least once every week or two.

Never mix cleaners. The CDC warns: never mix bleach with ammonia or other cleaners. Bleach and vinegar together give off chlorine gas, as explained in our vinegar vs bleach for mold guide.

If mold is growing deep inside the coils or fan housing where you can't reach, the unit may be past cleaning. That is a judgment call, and replacing a small portable unit may be simpler than taking it apart.

Texas humidity comes from the Gulf. NOAA's state climate summary for Texas says the Gulf serves as the primary source of moisture for the state, and that moisture is most available to eastern Texas. Annual rain ranges from less than 10 inches in the far west to more than 60 inches in the extreme southeast.

So a dehumidifier matters most in Houston, Beaumont, Corpus Christi and the rest of the coast, and much less in El Paso or Lubbock. Floods raise the stakes. During Hurricane Harvey in 2017, rainfall exceeded 30 inches in many locations, and catastrophic flooding hit much of southeast Texas. After any flood, the 24 to 48 hour drying window is the reason to run fans and dehumidifiers right away, once the power is safe.

Your air conditioner also dehumidifies, and the EPA lists air conditioners alongside dehumidifiers as a way to reduce humidity. A portable dehumidifier helps most in rooms the AC doesn't dry well: closets, laundry rooms, bathrooms without fans, garages turned into living space and rooms that flooded.

Call a professional if:

• Mold covers more than about 10 square feet. The EPA's home guide says you can usually handle a patch less than about 10 square feet (less than roughly a 3 ft. by 3 ft. patch); beyond that, or with a lot of water damage, it points to professional remediation guidance.
• Water came from sewage or floodwater. If damage was caused by sewage or other contaminated water, the EPA says to call in a professional experienced with that kind of damage.
• You smell mold but can't find it. The EPA notes mold can hide on the back side of dry wall, wallpaper, or paneling.

In Texas, mold jobs of 25 contiguous square feet or more generally call for a licensed contractor; TDLR says smaller areas may be cleaned or removed by people who are not licensed. Find a mold removal company in Houston or Corpus Christi, or a separate mold testing company if you need an assessment first. Texas law says a license holder may not perform both mold assessment and mold remediation on the same project. Check any license with our license check, browse all Texas cities, or read how mold remediation cost adds up.