A smell in the house: finding the cause
Musty
EPA: "You may suspect hidden mold if a building smells moldy, but you cannot see the source, or if you know there has been water damage and residents are reporting health problems." "There are many types of mold, and none of them will grow without water or moisture."1
What helps, EPA: "If possible, keep indoor humidity below 60 percent (ideally between 30 and 50 percent) relative humidity."1
EPA's guide to air cleaners: "Can portable air cleaners and furnace/HVAC filters solve mold problems? No. Portable air cleaners and furnace/HVAC filters do not address the cause of mold and musty odors. Mold is caused by a water or moisture problem in the building that allows the mold to grow."2
Paint, cleaner, or chemical
EPA: "Volatile organic compounds (VOCs) are emitted as gases from certain solids or liquids." "Paints, varnishes and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing and hobby products." "Concentrations of many VOCs are consistently higher indoors (up to ten times higher) than outdoors."3
What helps, EPA: "Increase ventilation when using products that emit VOCs." "Meet or exceed any label precautions."3
Sewer or rotten eggs
Connecticut's Office of Consumer Counsel: "If the air smells like rotten eggs, leave the area immediately and call 911."4
Wisconsin's health department, on sewer gas: "Hydrogen sulfide smells like rotten eggs, even in low concentrations." "Sewer gas can enter a home through a floor drain, from a leaking or blocked plumbing roof vent, or (if the gases are in soil next to the house) through cracks in the foundation."5
To keep it out: "Flush floor and sink drains with water to prevent the traps in sewer pipes from drying out."5
What you cannot smell
EPA: "Carbon monoxide is an odorless, colorless and toxic gas."6 What helps: "The U.S. Consumer Product Safety Commission (CPSC) recommends that every home have carbon monoxide (CO) alarms on each level outside each sleeping area."6
Radon. EPA: "You can't see radon. And you can't smell it or taste it." "The only way to know if your home has a radon problem is to test it."7 Find a test kit near you, then read your result.
A monitor for the air inside
Airthings View Plus: $329.99
Price checked October 1, 2026
Airthings says:8
- "Volatile organic compounds (VOCs) are airborne chemicals released by cleaning products, paint, new furniture, and adhesives."
- "Indoor humidity above 60% encourages mold growth and dust mites, while levels below 30% cause dry skin and throat irritation."
- "PM2.5 is fine particulate matter small enough to reach deep into the lungs."
The small commission from purchases made through this link helps keep this free public directory open, at no extra cost to you.
Filtering what is left
Airthings Renew
Airthings says:9
- "Activated charcoal filter. Captures and holds gases (VOCs) and odors."
EPA: "Note that there are no widely used performance rating systems for portable air cleaners or filters designed to remove gases."2
The small commission from purchases made through this link helps keep this free public directory open, at no extra cost to you.
EPA: "EPA neither certifies nor recommends particular brands of air filters or home air-cleaning devices including portable air cleaners or purifiers."2
Sources
- EPA, A Brief Guide to Mold, Moisture and Your Home, checked October 4, 2026
- EPA, Guide to Air Cleaners in the Home, checked October 4, 2026
- EPA, Volatile Organic Compounds' Impact on Indoor Air Quality, checked October 4, 2026
- Connecticut Office of Consumer Counsel, Natural gas safety, checked October 4, 2026
- Wisconsin Department of Health Services, Air: Sewer Gas, checked October 4, 2026
- EPA, Carbon Monoxide's Impact on Indoor Air Quality, checked October 4, 2026
- EPA, A Citizen's Guide to Radon (PDF), pages 3 and 13, checked October 4, 2026
- Airthings, View Plus product page, checked October 4, 2026
- Airthings, Renew product page, checked October 4, 2026