How to Find and Fix a Mystery Smell in the House

Step by step

1. 1

   Name the smell

   Stand where it is strongest and describe it. If a room smells moldy and you cannot see why, the EPA says to suspect hidden mold. A sewer or rotten egg smell right at a drain often comes from the drain, says the City of Phoenix, but rule out gas first. Spoiled food points to the fridge.

2. 2

   Walk it room by room

   Walk slowly through each room, opening closets and cabinets and getting down low near floor drains and under sinks. Note the spots where it is strongest.

3. 3

   Pour water into quiet drains

   Pour about a quart of water into every drain that does not get used much: a guest tub, a spare sink, a basement floor drain. The City of Phoenix explains that the water sitting in the curved pipe under each drain blocks sewer gas, and it can dry up when the drain sits unused. A quart is enough to refill it.

4. 4

   Do the glass test on a sink smell

   Fill a glass with cold water from the smelly sink, carry it to another room and sniff it. The City of Phoenix says if the water in the glass has no smell, the problem is the drain, not the water.

1. 5

   Clean the drain slime

   The City of Phoenix says hair, dirt and grime build a layer of slime in drains that gives off a rotten egg, sulfur smell. Pull the stopper, wipe off the gunk, and run a plastic hair snake down to pull up what is below. Our drain page shows how.

   What it looks like: a layer of slime on the stopper and on the snake.

2. 6

   Check the kitchen trio

   Open the fridge, toss anything spoiled and wipe up spills, as Whirlpool advises, and clean under the fridge too. Then pull out the dishwasher filter and rinse it, since Whirlpool lists unpleasant odors as a sign it needs cleaning. Last, check the garbage disposal (our disposal page has the steps).

3. 7

   Check the washer

   Smell the washer drum and the door seal. Whirlpool says to run a clean cycle at least once a month or every 30 cycles, and to leave the door or lid open between uses. It also says too much detergent builds up residue that can smell.

4. 8

   Measure the damp

   If the smell is musty, set a humidity meter in that room for a day. The EPA says to keep indoor humidity below 60 percent, and ideally between 30 and 50 percent. It also says hidden mold can grow on the back side of drywall, wallpaper or paneling.

   What it looks like: a reading over 60 percent means the room is damper than the EPA’s limit.

5. 9

   Fix the source, then air it out

   Once you find the source, fix that and air out the house. For a fridge smell that hangs on, Whirlpool suggests two open boxes of baking soda, one in the fridge and one in the freezer. Save the air freshener for after the cause is gone.

When it will not work, and what to do instead

Some smells are a job for a pro.

• Rotten eggs or a gas smell. Leave and call from a safe distance. Black Hills Energy says never to try to fix or adjust gas lines yourself.
• Mold that covers more than about 10 square feet, or mold hiding inside walls. The EPA says you can usually handle a smaller patch yourself. For bigger or hidden mold, it says to consider an experienced professional.
• The smell came with sewage or other dirty water. The EPA says to call a professional with experience cleaning up after contaminated water.
• You think mold is in the heating or cooling system. The EPA says not to run the system if you suspect mold in it.
• The sewer smell is back even with full drains. The City of Phoenix says a plumber can run a smoke test to find a leaking vent pipe.

Why it works

Most of the smells on this page come from one of three things: water that dried up, water that never dries, or food that went bad.

The dried up kind is the drain trap. The water in that curved pipe works like a cork that keeps the sewer smell down in the sewer. When nobody uses the drain, the cork slowly evaporates, and the smell comes right up.

The never dries kind is damp. Mold needs moisture, which is why the EPA says the fix for mold is fixing the water problem. Bring the damp down and the mold has nothing to grow on.

You walk in after a long day, and there it is again, that smell you cannot place. You light a candle, and by tomorrow it is back.