1. Eliminate Clutter
Cast a critical eye on household clutter, and pare down your stuff. Clutter blocks airflow and prevents your HVAC system from circulating air. Furniture and draperies that block supply grilles cause condensation. All this moisture creates microclimates in your home that welcome and feed mold growth.
So throw out things you don’t love or don’t use. Push furniture away from vents and grilles to keep air circulating. On humid, still days, run a couple of fans to keep air moving.
2. Control Indoor Climate
Mold problems often emerge during hot, humid summers when you’re tempted to play with the air conditioner. But set the thermostat too high, and the air conditioner won’t dehumidify your air effectively; set it too low, and you create cold surfaces where water vapor can condense.
To prevent moisture problems and maximize energy efficiency, set the thermostat at 78 degrees F.
3. Shut Windows and Doors When AC Is On
When you open windows and doors, you let air conditioning escape, waste money, and invite humid air into your cooler home. This causes condensation, which mold loves. So keep doors and windows shut when the AC is humming.
Also, maintain your home at around 80 degrees when you’re on vacation or at work. Too often, we bump the thermostat up to 85 degrees, or turn off the AC when we’re away. This raises temperature and humidity, which creates the ideal home for mold.
4. Properly Size Your AC Unit
Make sure your air-conditioning unit is properly sized for your house. If it’s too small, the unit will run constantly, elevating costs but not the temperature; too big, and the unit will constantly start and stop, which wastes energy, too.
Install an HVAC unit that’s just right. For guidance, call an HVAC professional or consult Energy Star’s square footage/AC capacity chart.
5. Monitor Humidity
An indoor humidity monitor will help you keep track of moisture levels that, ideally, fall between 35% and 50% relative humidity; in very humid climates, at the height of summer, you may have to live with readings closer to 55%.
But if you reach 60% relative humidity, it’s time to look for the source of the added moisture; above 70% relative humidity, certain species of mold can begin growing.
Indoor humidity monitors start at less than $20; more sophisticated models that simultaneously and remotely track several rooms can climb to $200.
6. Evaluate Your AC
If you get a high humidity reading of 60% or more, make sure your air conditioner is doing its job.
- Is it set to the proper temperature?
- Is it cycling on and off periodically?
- Does it blow cold air when it reaches the set point?
- Are the coils clean?
Inspect the condensate drain pipe (the narrow white pipe sticking out the side) to make sure it’s dripping regularly. If it isn’t, the pipe is blocked and water may be accumulating inside the unit — or on your floor. If you suspect a problem, call your HVAC professional. To prevent blockage and mold buildup, pour a cup of bleach mixed with water down the drain annually.
Related: HVAC Maintenance Checklist
7. Look for Standing Water
If the air conditioner isn’t the issue, search for standing water or chronic dampness that’s increasing indoor humidity and providing a lovely environment for mold.
Check for puddles or dampness around hot water tanks, sump pumps, freezers, refrigerators, basement doors, and windows. Inspect crawl spaces for ground water dampness or foundation leaks.
8. Cover Your Crawl Space Floor
Groundwater seeping into crawl spaces can add gallons of moisture vapor into your house every day. The simplest defense is to cover crawl space floors with a plastic vapor barrier — 6 mil polyethylene (landscapers’ plastic) — that traps moisture in the ground.
If you regularly crawl in your crawl space, use a heavier plastic that won’t rip as easily: Some 20 mil plastic coverings are on the market.
9. Add a Dehumidifier
A dehumidifier removes excess moisture from the air.
You can buy a whole house dehumidifier ($1,100-$1,800) that attaches to your furnace, treats air throughout the house, and connects to a drain so you never have to empty a tank. If you live in a very humid area, a whole-house system is the way to go.
If you have occasional bouts of dampness and musty smells, a portable dehumidifier will suffice ($150-$200).
Most models have an auto shutoff that keeps the unit from overflowing when the storage tank is full. Some portables have a hose hookup that automatically sends water into a nearby floor drain.
10. Call a Professional
If you can’t find the moisture problem on your own, or you aren’t sure how to correct a problem you do find, call a home inspector or indoor air quality consultant. Look for credentials from a respected industry organization, such as the American Society of Home Inspectors or the Indoor Air Quality Association. A house call will likely run $250 or more.