Signs You Might Need a Dehumidifier

White dehumidifier machine next to house plant on green plant stand

The Spruce / Almar Creative

It is important to maintain a proper humidity level in your home. While too little humidity can cause some discomfort issues such as chapped lips as well as cracks in wooden furniture, the reverse—too much moisture—can make your home a breeding ground for mold and mildew. A dehumidifier can help you remedy excess moisture problems.

You can more accurately measure your home's humidity level with a hygrometer and then take appropriate action to either add humidity with a humidifier or remove moisture with a dehumidifier. While a hygrometer is a very handy instrument for controlling home moisture, there is a tendency to only measure certain living areas, thus omitting some corners where moisture problems can take hold.

Some homes may have moisture problems only at certain times of the year, such as in spring when there is a lot of groundwater runoff, while other residences need help to control moisture levels year-round. There are also times when moisture is a problem only in one room or area of the home and though small, this should not be neglected.

What Is Groundwater Runoff?

Water runoff is the process of water moving across the soil and potentially causing flooding and other damage, rather than being absorbed down into the earth. Runoff generally occurs when the soil is already completely saturated, such as in the spring due to snow melt and frequent rains.

Once excessive moisture is detected, the first plan of action should be to discontinue any use of humidifiers if these are in use or to try and remove what is causing the humidity. Further action should be taken to find the cause and remedy the situation.

Learn the most common signals when excessive humidity is present.

  • 01 of 05

    Window and Patio Door Condensation

    Condensation on interior window glass closeup

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    Condensation on the interior glass, water beading on a window or the presence of what looks like a fog or vapor on the glass are typical signs that there is too much moisture in the room. 

    This often happens when a humidifier is too large for the room and puts out too much humidity. A build-up of moisture on a window sill can eventually rot wooden casings and that wetness will allow mold to grow. Mold will look like a black or dark grunge on the bottom window trim, or in the track of a patio door.

    Immediately turn off any humidifier that is operating and in the future, downgrade the unit to reduce the amount of moisture output. When too much humidifier output is the cause, the moisture level may correct itself simply by stopping humidifier use and opening a window to add air circulation to the room.

    Another thing that can cause moisture buildup on windows is humidity present in the construction materials of the home such as with improper sealing of sheetrock walls or humidity that is present in cement.

    The outdoor climate can also cause some indoor moisture problems, such as when it rains for several days or the area where you live has a high humidity factor. A dehumidifier will effectively remove the moisture from the home and restore proper indoor levels. Remember to rotate the dehumidifier through all the areas affected by excess humidity.

  • 02 of 05

    Mold Spots on Ceiling or in Corners of Walls

    Mold on ceiling
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    Since steam rises, bathroom moisture problems are often found on ceilings or up in the corners of the walls. Bathrooms that do not have efficient fans to divert steam and humidity to the outdoors, most often have some problems with mold. 

    Mold can grow on the wall, ceiling, under or around the toilet, or behind the bath or shower surround. A leaky toilet or plumbing can also cause moisture problems.


    Excess moisture can cause black mold to grow. You do not have to see the mold for it to affect you; it just has to be present somewhere.

    Running a dehumidifier in these areas can help, but remember that while this is necessary, you have to get at the root of the problem to find a long term solution. A dehumidifier will lessen the amount of moisture damage but the cause cannot be ignored.

    For those finding a repair solution for excess moisture such as removing mold and repairing walls, you must use a paint that is specially formulated to resist mildew and seal those areas that have been repaired. Otherwise, mold will find its way back through layers of regular paint and be noticeable once again.

    Other areas of the home often affected by trapped moisture are closets, garages or basement rooms and storage areas. You might also see dripping or mold spots below the windows. This can be caused by faulty window seals or rotting casings. In this case, windows should be replaced along with frames and sheetrock and insulation changed to remove all wet areas.

  • 03 of 05

    Musty Smell or Odor

    Attic crawl space with boxes causing musty odor

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    The presence of a musty odor in basements, crawl spaces, entrances, and garages may signal the presence of mold and mildew. Moisture could have been a one-time event or a recurring problem.

    Possible causes range from an improper window or door seal, construction sealing issues to wet basement areas from high groundwater seepage, which can be a natural occurrence in your particular locale or by inadequate weeping ​tile installation around the home.​​​​

    Anytime there is a musty smell, there is mold somewhere. A dehumidifier can help with immediate moisture removal, but you will have to investigate further and remedy the situation to not have recurring problems. In all likelihood, those areas will also require heat to help dry the affected space.

    In the laundry room, a musty odor in the air, or musty smelling towels or bedding could signal problems with a high-efficiency (HE) or front-load washer. Though more efficient in many ways compared to a traditional top-load washer, front-loading washers are more likely to have mold issues. 

    There have been many advances by manufacturers to reduce the risk of mold in front load washers since they were first introduced to the market, but consumers need to know that it can still happen. Mold issues are not specific to a particular brand, though some washers have been redesigned and are better than others. (Learn the differences between a top-load washer and a high-efficiency front-load washing machine.)

    A musty odor in the laundry room can also be caused by a plugged exterior vent or an interior dryer lint filter that has been neglected and is impacted with lint. This can cause moist air from within the dryer when drying a wash load, to become trapped since there is no clear, unobstructed airflow, resulting in a musty smell. Plugged lint filters, in or outdoors, can also become ​a fire hazard. They should be cleared of lint—the interior dryer lint filter should be emptied after each dryer load; the exterior lint filter should be cleared as required.

  • 04 of 05

    Recurring Spring Water Run-Off Dampness

    Springwater dampness with grayish water marks on wall

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    If spring groundwater dampness has become a recurring problem or you have purchased a home that has white or grayish water level marks in the basement, a dehumidifier can help to remove the extra moisture should these events occur.​

    It would also be a good idea to investigate why your basement is prone to water, which may be from inadequate weeping tiles around the home, concrete that may need to be re-parsed and sealed, or it may simply be because the house was built on a historical river bed or low plain.

    Continue to 5 of 5 below.
  • 05 of 05

    Inspect for Mold, Water Stain Marks When Buying a Home

    Keys being handed over after buying a home

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    Whether you are buying a home or RV, you should always look for signs of excess moisture problems. Tell-tale signs that a home has had water problems are mold or mildew in corners of walls or ceilings in any rooms, including the bathroom, and water level marks in the basement.

    Look inside closets at the walls, behind furniture at baseboards, around and below windows for evidence of mold or water stain marks and be on the lookout for musty smells. It is not uncommon for some people to give their home a fresh coat of paint to mask potential problems when it goes up for sale. A fresh coat of paint can make it harder to detect water problems but look inside closets and inspect the foundation and basement. A home that is overly fragranced often may have something to hide when it comes to odors or mold.

    If you do encounter noticeable water problems, be sure to ask why and if remedial action was undertaken. You may want to bring in an expert to confirm or allay your fears and give you an estimate of possible costs to remedy the situation.

Article Sources
The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Mold. Centers for Disease Control and Prevention.

  2. Mold. Centers for Disease Control and Prevention

  3. Clothes Dryer Fire Safety Outreach Materials. U.S. Fire Administration.