A musty smell in your house usually means moisture is feeding mold or mildew somewhere you cannot see. Common sources are a hidden plumbing leak, an AC drain pan or ducts, an evaporative cooler, wet carpet pad, or a home that sat closed up. Find the moisture, dry it and clean it. Air fresheners only hide the smell.
Key takeaways
- Musty means moisture. Treat the smell as a clue to a water problem.
- Check under sinks, around the AC, behind the washer and along floors first.
- A rotten-egg smell is different. That points to sewer gas, not mold.
- If the smell returns after cleaning, the moisture source is still there.
What causes a musty smell in a house?
That earthy, damp-basement odor comes from compounds released by mold and mildew as they grow. They need moisture to grow, so the smell is really pointing you to water. These are the usual suspects in East Valley homes:
| Source | Where to look | Clue |
|---|---|---|
| Hidden plumbing leak | Sink cabinets, behind toilets, walls behind showers | Smell is strongest in one room |
| AC drain pan or ducts | Air handler closet, attic, return vents | Smell is strongest when the AC turns on |
| Evaporative (swamp) cooler | Cooler pads, water reservoir, ducts | Smell blows from vents when the cooler runs |
| Wet carpet pad | Rooms near bathrooms, laundry or exterior doors | Smell is strongest near the floor |
| Slab leak | Floors with warm or damp spots | Smell plus a rising water bill |
| Washing machine | Front-load door gasket and detergent drawer | Smell is strongest in the laundry room |
| Closed-up seasonal home | Whole house after months away | Smell hits when you open the door |
| Under a manufactured home | Belly wrap and subfloor | Soft floors plus odor |
How do you find the source of a musty smell?
- Do a room-by-room sniff test. Close the doors for an hour, then open each room and note where the smell is strongest.
- Turn the AC or cooler off, then on. If the smell jumps when air starts moving, check the drain pan, coil, cooler pads and ducts.
- Open every sink cabinet. Look and feel for damp wood, swollen particleboard or water stains.
- Pull appliances out. Check behind the refrigerator, dishwasher and washing machine.
- Check the floors. Press on carpet near walls and look for warped laminate or loose tile.
- Run a water meter test to rule out a hidden leak. Our guide to signs of water damage in walls shows how.
Is a musty smell the same as sewer gas?
No. A musty smell is earthy and damp. Sewer gas smells like rotten eggs. Sewer gas often comes from a dry drain trap in a rarely used sink or shower, a failed toilet wax seal, or a vent problem. Run water in unused drains to refill the traps. If the rotten-egg smell persists, call a plumber. If you smell gas like natural gas or propane, leave the home and call your gas utility.
Musty smell and a damp spot you can't explain? Get moisture mapped before the mold spreads.
Call: (856) 481-6893How do you get rid of a musty smell for good?
- Fix the water source. Repair the leak, clear the AC drain, or service the cooler.
- Remove what cannot be saved. Moldy carpet pad, drywall and particleboard usually have to go.
- Clean hard surfaces with detergent and water, then dry them completely.
- Dry and dehumidify. Bring humidity down and keep it under 60 percent.
- Change filters. Replace the AC filter and cooler pads, and clean registers.
- Air it out. Ventilate once the moisture source is fixed.
If the smell comes back, moisture is still present. Read how fast mold grows after water damage to judge how far it may have spread.
Why do homes smell musty after summer?
Many Apache Junction and Gold Canyon owners leave for the hot months. Our snowbird leak checklist covers what to do before you go. If a toilet runs, a supply line drips or the AC drain backs up while the house is closed, there is nothing to dry it. Turning the AC way up or off adds heat and humidity. Owners often come home in the fall to a musty smell that started with a small leak in July. A neighbor check after big storms and a shut-off main valve prevent most of these surprises.