Heat gets the attention in summer, but humidity often does more to make a house uncomfortable. Damp air feels warmer than it is, encourages mold and dust mites and can leave a home smelling stale. Your first summer is a good time to learn how your house handles moisture, because small fixes made now can prevent bigger problems later.
Signs your home is too humid
- A sticky or clammy feel indoors, even with the air conditioning running
- Musty smells, especially in basements, closets and bathrooms
- Condensation on windows, cold water pipes or the outside of toilet tanks
- Mildew on bathroom ceilings, grout or window frames
- Warped wood, peeling paint or doors that begin to stick
An inexpensive hygrometer, a small device that measures relative humidity, takes the guesswork out. Place one in the main living area and another in the basement, if you have one, and watch the readings for a few weeks. The Environmental Protection Agency recommends keeping indoor humidity in a moderate range to discourage mold, so a meter that regularly reads high is worth investigating.
Common causes
Moisture comes from inside and out. Showers, cooking, laundry and even houseplants add water to the air every day. From outside, humid air leaks in through gaps, and groundwater can seep into basements and crawl spaces. Clothes dryers or bathroom fans that vent into the attic or crawl space instead of outdoors are a common hidden source.
The air conditioner plays a role too. A properly working system removes moisture as it cools. A system that is too large for the house may cool quickly and shut off before it has removed much humidity, leaving rooms cool but clammy. A clogged filter, a dirty coil or a blocked condensate drain can also reduce how well it dries the air.
Simple fixes to try first
- Run bathroom exhaust fans during showers and for a while afterward, and use the range hood when cooking.
- Make sure the dryer vents outdoors and that the lint screen and vent duct are clean.
- Keep gutters clear and downspouts directed away from the foundation.
- Close windows on humid days and let the air conditioning do its work.
- Change the HVAC filter on schedule.
- Use a portable dehumidifier in a damp basement, and empty or drain it regularly.
When to call a professional
If humidity stays high despite these steps, or you see spreading mold, standing water or wood that feels soft, bring in help. An HVAC technician can check whether the system is sized and set up to control moisture and whether a whole-house dehumidifier makes sense. A waterproofing contractor can evaluate a wet basement or crawl space. If anyone in your household has asthma, allergies or other health concerns that mold could affect, talk with a doctor as well.
Controlling moisture is one of the quiet skills of homeownership. Once you know your home’s patterns, a few steady habits keep it comfortable all summer.
A Four-Week Humidity Check for Your First Summer
Learning how your home handles moisture is easier with a simple, structured routine. Here is one approach for the first month of summer in a new house.
Week one: measure
- Place a hygrometer in the main living area, a bedroom and the basement or lowest level.
- Write down the readings each morning and evening, along with whether the air conditioning was running and what the weather was like.
- Note any rooms that feel clammier than others, or smell musty when you first walk in.
Week two: look for sources
- Check that bathroom fans actually pull air. Hold a single square of tissue near the grille; it should be drawn toward the fan.
- Follow the dryer vent from the machine to the exterior and confirm the outside flap opens when the dryer runs.
- Walk around the outside after a rain and see where water collects near the foundation.
- Look at the condensate drain line where it exits the house to confirm it is draining during cooling.
Week three: make simple changes
- Run exhaust fans longer after showers and cooking.
- Extend downspouts and clear gutters if water is pooling near the house.
- Move a portable dehumidifier into the dampest space and set it to a moderate level.
- Replace the HVAC filter if it has been a while.
Week four: compare
- Look at your readings again. If they have improved, keep the new habits.
- If humidity is still high, schedule an HVAC technician or other professional and share your notes with them.
Humidity Mistakes New Homeowners Make
- Opening windows on humid days to “air out” the house. In muggy weather, this can bring more moisture inside than it removes.
- Turning off the air conditioning while away for long periods. In humid climates, letting the house sit without any cooling can allow moisture to build up. A higher thermostat setting is often a better approach than turning the system off entirely.
- Painting over mildew. Paint does not solve the moisture problem underneath. Clean the area according to product directions and address the cause.
- Ignoring the crawl space. Moisture under the house can affect the air and the wood framing above it. If you have a crawl space, have it looked at during your first year.
- Letting the dehumidifier fill up. A full bucket usually means the unit has stopped working. Empty it often or set it up to drain continuously if the model allows.
- Storing boxes directly on a basement floor. Cardboard absorbs moisture. Use shelves or plastic bins in damp spaces.
Questions Homeowners Ask About Humidity
Can indoor air be too dry in summer?
It is less common in humid climates, but it can happen in some homes. A hygrometer will tell you, and the goal is a moderate, comfortable range rather than the lowest possible reading.
Does a whole-house dehumidifier make sense?
For some homes, especially those with persistent moisture or large below-grade spaces, a whole-house system connected to the HVAC can help. An HVAC professional can tell you whether your home would benefit.
How do I clean small areas of mildew?
Small spots on hard surfaces can often be cleaned with appropriate household cleaning products, following the label directions and with good ventilation. Larger areas, or mold that keeps returning, are a reason to call a professional.
Can plants and aquariums raise humidity?
They can add some moisture to the air, especially in large numbers. If a room with many plants or an aquarium reads consistently high, try running a fan or dehumidifier nearby.
