What Are the Signs of Poor Indoor Air Quality?

The most telling sign of an indoor air quality problem is health symptoms that correlate with time spent at home. If you or a family member experiences persistent sneezing, runny nose, itchy eyes, coughing, or worsening asthma symptoms — and those symptoms improve noticeably when you spend time away from home — the air inside your home is worth investigating.

Headaches, fatigue, and difficulty concentrating can also be related to indoor air quality, particularly in homes with elevated carbon dioxide levels from inadequate ventilation or in homes with off-gassing from new furniture, flooring, or paint. These symptoms are often dismissed as unrelated, but the pattern of feeling better away from home is a consistent indicator.

A musty or earthy smell is one of the most reliable indicators of mold or mildew growth somewhere in the home — often in the ductwork, in a crawl space, or behind walls near plumbing. Mold does not always have to be visible to affect air quality. HVAC systems can distribute mold spores throughout the entire home if growth is present in or near the air handler or ductwork.

Chemical or plastic odors, particularly in newer homes or after renovations, often indicate off-gassing from building materials, adhesives, or furnishings. These volatile organic compounds (VOCs) can cause irritation and, in high concentrations, more serious health effects. A stale or stuffy smell that persists even with windows open points to inadequate ventilation — the home is not exchanging enough air with the outside.

If dust accumulates on surfaces faster than seems normal, or if you can see dust particles floating in sunlight coming through a window, the home's air filtration is likely inadequate. Standard 1-inch fiberglass filters capture large particles but allow fine dust, pollen, pet dander, and other allergens to circulate freely. Upgrading to a higher-MERV filter or adding a whole-home air cleaner can make a significant difference.

Dusty supply registers or visible debris around return air vents are also signs that the filtration system is not keeping up. If the ductwork has not been cleaned in many years and the home has had renovations, pets, or water intrusion, accumulated debris in the ducts can be a source of ongoing particulate contamination.

Both low and high humidity cause indoor air quality problems, and both are common in Indianapolis homes. In winter, forced-air heating systems dry the air significantly — relative humidity in heated homes often drops to 20% to 30%, well below the 35% to 50% range recommended for comfort and health. Dry air causes dry skin, irritated nasal passages, increased susceptibility to respiratory infections, and static electricity. It also causes wood floors, furniture, and trim to shrink and crack.

In summer, high humidity creates conditions favorable for mold and dust mite growth. Relative humidity above 60% indoors is a risk factor for mold, and dust mites thrive above 50%. If your home feels clammy, if condensation forms on windows, or if you notice a musty smell during humid weather, the home may need better moisture control — through improved ventilation, a whole-home dehumidifier, or addressing the source of moisture intrusion.

Visible mold growth — whether black spots on bathroom grout, discoloration on ceiling tiles, or growth around window frames — is a direct indicator of an air quality problem. Mold releases spores into the air that can cause respiratory irritation, allergic reactions, and in sensitive individuals, more serious health effects. Visible mold is always worth addressing, and the underlying moisture source needs to be corrected or the mold will return.

Water stains on ceilings or walls, even old ones, indicate past or ongoing moisture intrusion that may have led to mold growth inside wall cavities or above ceiling tiles. If you see staining near HVAC supply or return vents, the system itself may be a source of moisture or mold distribution.

The starting point is identifying the source of the problem. An HVAC technician can inspect your air handler, ductwork, and filtration system and identify whether the HVAC system is contributing to air quality issues. Common solutions include upgrading to a higher-efficiency air filter, installing a whole-home air purifier or UV system, adding a whole-home humidifier or dehumidifier, or having the ductwork inspected and cleaned.

Improving ventilation is also important. Modern homes are built tightly for energy efficiency, which means they do not naturally exchange air with the outside the way older homes do. A heat recovery ventilator (HRV) or energy recovery ventilator (ERV) brings in fresh outdoor air while recovering most of the heating or cooling energy from the outgoing air — improving air quality without significantly increasing energy costs.