IAQ stands for indoor air quality — a term that describes the condition of the air inside a building in terms of its health and comfort impact on occupants. It encompasses the concentration of pollutants (particulates, gases, and biological contaminants), humidity levels, ventilation adequacy, and temperature consistency. The EPA has found that indoor air can be two to five times more polluted than outdoor air — sometimes significantly more — largely because modern homes are built to be tightly sealed for energy efficiency, which concentrates whatever enters or off-gasses inside.

Why IAQ Matters for Colorado Homeowners

Denver and the Front Range have a specific set of indoor air quality challenges that make IAQ more than an abstract concern. Colorado’s very dry climate — typically 20–40% relative humidity year-round — dries out mucous membranes, making respiratory systems more vulnerable to airborne irritants and increasing static electricity that can affect electronics. Wildfire smoke season, increasingly common and intense across the Mountain West, pushes fine particulates (PM2.5) indoors even with windows closed — particles that standard fiberglass filters allow to pass through freely. High-altitude UV radiation accelerates off-gassing from certain building materials and furniture. And Colorado has one of the highest average indoor radon concentrations in the country, driven by uranium-rich soils common across the state.

The Main Categories of Indoor Air Pollutants

IAQ problems generally fall into a few categories:

  • Particulate matter: Dust, pollen, pet dander, mold spores, skin cells, and wildfire smoke particles. Measured in microns — PM2.5 (2.5 micrometers or smaller) poses the greatest health risk because particles this size penetrate deep into the lungs.
  • Biological contaminants: Mold, bacteria, viruses, dust mites, and pet allergens. These thrive in humid environments but mold can also grow on HVAC coils and inside ductwork even in dry climates.
  • Chemical pollutants (VOCs): Volatile organic compounds off-gassed from paints, adhesives, flooring, cleaning products, and furniture. New construction and recent renovations often have elevated VOC levels for months.
  • Combustion gases: Carbon monoxide (CO) and nitrogen dioxide from gas appliances, fireplaces, and attached garages. At Denver’s altitude, gas appliance combustion is less efficient than at sea level, which can increase CO risk if appliances aren’t properly maintained and vented.
  • Radon: A naturally occurring radioactive gas that enters homes through foundation cracks and soil contact. Colorado’s geology makes radon testing particularly important here.

How HVAC Systems Affect IAQ

Your heating and cooling system plays a central role in IAQ — for better or worse. A well-maintained system with a high-quality filter removes particulates from circulating air, controls humidity (via the evaporator coil during cooling), and distributes fresh ventilation air if the system is connected to fresh-air intake. A poorly maintained system does the opposite: a dirty filter allows pollutants to bypass filtration; dirty coils and ductwork distribute accumulated mold and biological debris; inadequate ventilation lets pollutant concentrations rise unchecked. This is why IAQ and HVAC maintenance are closely linked — the system you rely on for comfort is also your first line of defense for air quality.

IAQ Solutions That Work

Improving IAQ doesn’t require a single expensive fix. A layered approach is most effective: a higher-MERV air filter to capture more particulates, a UV germicidal light to address biological contaminants on the evaporator coil, a whole-house humidifier to bring Colorado’s dry indoor air to a healthier 35–50% relative humidity, and a ventilation strategy (ERV, HRV, or controlled fresh air intake) to dilute indoor pollutant concentrations. For wildfire smoke specifically, a portable HEPA air purifier in bedrooms provides targeted protection during smoke events. Radon requires its own mitigation system — a sub-slab depressurization system installed by a certified contractor.

Getting Your IAQ Assessed

The right starting point is understanding what’s actually in your air before investing in equipment. Done can evaluate your home’s IAQ, identify the specific pollutants or conditions that are most relevant to your situation, and recommend targeted solutions. Many IAQ improvements also deliver HVAC efficiency benefits — a clean system running with proper airflow uses less energy — so addressing air quality and equipment performance often go hand in hand.

Learn more about Done’s approach to indoor air quality. If ductwork is part of the equation, duct cleaning addresses accumulated contamination inside your distribution system. For humidification, filtration, and purification equipment, Done can assess and install the right solution for your home.