Why does my house feel stuffy?

A house usually feels stuffy for one of three reasons: not enough fresh air is getting in, the air holds too much moisture, or air is not moving well through the rooms. Most of the checks are free and take an afternoon. Start with humidity and the filter, then work through the list below.

Not enough fresh air

The EPA explains that if too little outdoor air enters indoors, pollutants can accumulate to levels that can pose health and comfort problems.^[1] Odors and moisture from cooking and showers build up when there is nowhere for them to go.

Your heating and cooling system probably does not help here. The EPA notes that most home heating and cooling systems, including forced air heating systems, do not mechanically bring fresh air into the house.^[2] They recirculate the same air. Fresh air comes in through leaks and open windows, which is why homes built to keep outdoor air from leaking in and out, without special mechanical ventilation, may have higher indoor pollutant levels.^[1] Well-sealed and recently weatherized houses often feel this way.

For a sense of scale, the EPA says ASHRAE recommends that homes get 0.35 air changes per hour but not less than 15 cubic feet of air per minute (cfm) per person^[3] as a minimum. You cannot measure that yourself, but an HVAC contractor can.

Leaks are not the answer either. Virginia Cooperative Extension points out that a leaky building is no assurance of good indoor air quality,^[4] and that natural ventilation is mostly unreliable and uncontrolled air movement^[4] that can bring moisture with it. Open windows help for an hour; they are not a ventilation system.

Too much humidity

Damp air feels heavy and warm even when the thermostat says otherwise. ENERGY STAR describes the first level of a damp space as "Slightly to Moderately Damp : space feels damp and has musty odor that may be intermittent. 50-75% relative humidity",^[5] and says the optimum RH level for a building is generally considered to be between 30% and 50%.^[5] The EPA's target is below 60 percent (ideally between 30 and 50 percent).^[6] Humidity also makes other problems worse: High temperature and humidity levels can also increase concentrations of some pollutants.^[1]

The usual sources are showers, cooking, laundry and a damp basement or crawl space. The EPA's simplest fix: Run the bathroom fan or open the window when showering.^[6] Check where that fan goes, though. Virginia Cooperative Extension says most building codes require bath and kitchen exhaust fans to vent to the outside, not just into an attic or crawl space,^[4] and a fan that dumps into the attic only moves the problem.

In a damp basement, a dehumidifier works best with the space closed off: Doors and windows to the space being dehumidified should be closed while the unit is running.^[5] ENERGY STAR says a whole-home dehumidifier carries significant benefits for relatively well sealed homes with central air systems that see humidity readings above 55% consistently throughout the house.^[5]

Air is not moving

Ducts. ENERGY STAR lists as a sign of poorly performing ducts that you have stuffy rooms that never seem to feel comfortable,^[7] and says about 20 to 30 percent of the air that moves through the duct system is lost due to leaks, holes, and poorly connected ducts.^[7] ENERGY STAR lists ducts located in an attic, crawlspace, or the garage as another warning sign.^[7] Where you can reach them safely from a basement or utility-room floor, ENERGY STAR says to seal air leaks using mastic sealant or metal tape,^[7] adding: "Never use duct tape, as it is not long-lasting."^[7]

Vents and doors. A closed register, a sofa over a floor vent, or a bedroom door kept shut with no return grille often leaves one room stale while the rest of the house is fine.

The filter. In the EPA's words, if a filter is dirty and overloaded, it won't work well.^[8] A clogged filter cuts airflow everywhere. See how often to change your furnace filter and which MERV rating to use.

A portable air purifier like this one catches dust and pollen, but it will not fix stale or humid air on its own.

Something is giving off fumes

New paint, a refinished floor, new furniture or a shelf of solvents can make a house feel close. The EPA lists short-term effects of indoor pollutants as irritation of the eyes, nose, and throat, headaches, dizziness, and fatigue.^[1] Its advice for telling indoor causes apart from a cold: If the symptoms fade or go away when a person is away from the area, for example, an effort should be made to identify indoor air sources that may be possible causes.^[1]

Carbon monoxide is a colorless, odorless gas,^[12] so you will not notice it as stuffiness, but its symptoms overlap. The EPA lists headaches, dizziness, sleepiness, coughing, and watery eyes^[9] among the symptoms of combustion pollutants. Make sure you have a working CO alarm in the hallway near every separate sleeping area.^[12]

Stop and call a pro if

• A CO alarm sounds, or people feel dizzy or sick at home. The EPA says to get fresh air immediately, open windows and doors, turn off any combustion appliances and leave the house,^[9] then get medical help and have the appliances inspected.
• You smell gas. Columbia Gas of Virginia says a sulfur or rotten-egg-like odor could mean a gas leak: get out immediately, do not use anything that could cause a spark, like a phone, light switch, appliance or flashlight, and call 911 and your gas company from a safe location away from the building.^[11]
• Humidity stays high while the air conditioning runs. That points to the system's sizing, airflow or drainage, which an HVAC technician should check.
• The vents smell musty. Do not keep running a system you think has mold in it; have it inspected.
• The ducts are wrapped in old tape, paper-like wrap or insulation. A heating and cooling system can contain asbestos-containing materials, such as insulation and register boots, and the EPA says those materials should not be disturbed or removed except by specially trained and equipped contractors.^[10] Do not cut, scrape or seal over old duct wrap you cannot identify; have it checked first.
• Reaching the ducts means crawling over attic joists or into a tight, wet crawl space. Leave that inspection to an HVAC contractor.
• One room never gets comfortable. Ducts are often hidden in walls and ceilings, and ENERGY STAR notes that most heating and cooling equipment contractors also repair ductwork.^[7]
• You want mechanical fresh-air ventilation or a whole-home dehumidifier. Virginia Cooperative Extension says a whole-house ventilation system must be correctly sized by a qualified or licensed HVAC company.^[4]

Getting help

For the full list of fixes, see how to improve indoor air quality at home, and if you want something measured, who to call to test your indoor air. Loclis lists DPOR-licensed HVAC businesses with their licence number and class: look up HVAC businesses in Blacksburg, browse indoor air quality services, or read all heating and cooling answers.

If the system or the ducts need a look, describe the problem once and licensed local HVAC businesses quote it.