Why does my house still smell after a deep clean?

A house that still smells after a deep clean usually has a source that was never on the cleaning list. The common ones are a dried-out drain trap letting sewer gas in, food built up inside the garbage disposal, a refrigerator that was wiped outside but not emptied, odors soaked into carpet, pads, mattresses and curtains, a dirty HVAC filter, and hidden moisture or mold. Sometimes the smell is the cleaning products themselves.

One smell is not a cleaning problem. Natural gas is colorless and odorless, so utilities add an odorant called mercaptan that smells like sulfur or rotten eggs.^[1] If you notice it, leave the house right away; do not use light switches, phones or anything that could spark,^[1] and call 911 and your gas utility once you are outside.

Start by naming the smell

The kind of smell points to the source, so walk the house room by room with fresh air in your nose and note where it is strongest.

• Chemical or perfumed: cleaning products and air fresheners.
• Sewer or rotten: a dry trap, a blocked vent, or the disposal.
• Sour or spoiled: the refrigerator, trash cans or the disposal.
• Musty or earthy: moisture and mold.
• Animal: urine or dander in carpet, pads and upholstery.
• Dusty or burnt when the heat comes on: the HVAC filter or dust in the system.

The cleaning products themselves

EPA lists cleansers and disinfectants, aerosol sprays, and moth repellents and air fresheners among the household products that release volatile organic compounds.^[5] A strong "clean" smell after a deep clean is often just that, and spraying air freshener on top adds more. EPA says that for most indoor air quality problems in the home, removing or controlling the source is the most effective solution.^[6]

Fresh air helps more than people expect. Most home heating and cooling systems, including forced-air systems, do not mechanically bring fresh air into the house.^[6] EPA notes that bathroom and kitchen fans that exhaust outdoors remove contaminants from the room and bring in more outdoor air.^[6] Open windows and run those fans for a few hours after a deep clean. If the chemical smell bothers you, ask your cleaner to use fewer or unscented products.

Drains, the disposal and the refrigerator

Dry traps. Every drain has a U-shaped trap that holds water to block sewer gas. A guest bathroom, a basement floor drain or a tub nobody uses can dry out. Fairfax County's public works department advises adding water regularly to plumbing fixtures, especially seldom-used sinks, toilets and floor drains,^[2] because sewer gas and odors can enter a home when the water in a fixture's trap has evaporated.^[2] If every trap is full and the smell persists, the county says the problem could be the plumbing vent that carries sewer gas out through the roof, which leaves or bird nests can plug.^[2] That vent is a job for a plumber, not a ladder.

The disposal. A disposal odor is usually a sign of food buildup, caused by too little water flow during and after use.^[3] Flush it with warm water and baking soda, and run cold water while grinding from now on. Never reach into a disposal.

The refrigerator. A cleaner may wipe the outside and leave the inside to you. FDA advises cleaning the refrigerator regularly and wiping spills immediately.^[4] Empty it, throw out anything doubtful, and wash the shelves and drawers.

Soft surfaces hold smells

Carpet, pads, mattresses, upholstery and curtains absorb smoke, cooking, pet and body odors, and a surface clean does not reach far into them. Launder what you can, vacuum slowly, and consider a professional carpet or upholstery clean. Pet urine that soaked through to the pad is a common reason a room smells after everything else is clean; see how to get pet stains out of carpet and why a carpet stain comes back.

Hidden moisture and mold

EPA advises that you suspect hidden mold if a home smells moldy but you cannot see the source, or if you know there has been water damage.^[7] It lists places mold hides, including the back side of drywall, wallpaper or paneling, the underside of carpets and pads, and inside walls.^[7] Absorbent materials such as carpet and ceiling tiles may have to be thrown away if they become moldy.^[7]

Humidity drives this. EPA's advice is to keep indoor humidity below 60 percent, ideally between 30 and 50 percent.^[7] A small humidity meter tells you where you stand. For mold that keeps returning in a bathroom, see why a bathroom keeps getting moldy.

Heating and cooling

ENERGY STAR advises that you inspect, clean or change the air filter in your furnace, central air conditioner or heat pump once a month.^[8] It also notes that a plugged condensate drain can cause water damage and affect indoor humidity.^[8] A smell that appears when the system starts, or that is strongest at the vents, points here. Dust also builds up quickly in some homes; see why a house gets dusty so fast.

Stop and call a pro if

• You smell sulfur or rotten eggs. Leave and call 911 and the gas utility from outside.
• Every drain trap is full and a sewer smell remains. A plumber can check the vent and the drain line.
• The smell is musty and you find stains, soft drywall, warped flooring or mold on more than a small area. The moisture needs to be found and fixed first.
• The smell comes from the HVAC system after you change the filter, or a condensate drain is overflowing. Call an HVAC technician.
• You smell burning plastic or electrical heat near an outlet, switch or appliance. Stop using it and call an electrician.

Getting help

If the smell traces back to carpet, upholstery or an old deep clean that missed areas, a cleaning business can help. Read how often to schedule a deep clean, browse deep cleaning businesses or cleaning services around Blacksburg, and see the rest of the cleaning answers. When you know what you need, describe the job on Loclis and businesses will quote.