Indoor Air Quality: How Your HVAC System Affects the Air You Breathe and How to Improve It

The EPA estimates that indoor air is 2-5 times more polluted than outdoor air, and Americans spend 90% of their time indoors. Your HVAC system circulates all the air in your home 5-7 times per day - making it the single most effective tool for improving or worsening indoor air quality. Here's how to make it work for you.

Common Indoor Air Pollutants

Dust and particulate matter: Skin cells, fabric fibers, pet dander, pollen, and general dust circulate continuously through your HVAC system. Standard 1-inch fiberglass filters catch only the largest particles. Biological contaminants: Mold spores, bacteria, dust mites, and viruses thrive in HVAC systems with poor maintenance, especially in the dark, humid environment of the evaporator coil and condensate drain. Volatile organic compounds (VOCs): Off-gassing from paint, furniture, cleaning products, and building materials. Carbon monoxide: From gas furnaces, water heaters, and attached garages. A cracked heat exchanger or blocked flue can allow CO into living spaces.

Your Air Filter: The First Line of Defense

Your HVAC filter is the primary air cleaning mechanism in your home, and most homeowners are using the wrong one. MERV 1-4 (basic fiberglass): Catches only large particles. Does almost nothing for air quality. Only protects the equipment itself. MERV 8-11 (pleated): The sweet spot for most homes. Catches dust, pollen, mold spores, and pet dander. Doesn't restrict airflow significantly on standard systems. MERV 13-16 (high-efficiency): Catches bacteria, smoke, and virus-carrying droplets. Excellent filtration but may restrict airflow on older or undersized systems. Confirm with your technician before upgrading. HEPA (MERV 17+): Hospital-grade filtration. Too restrictive for standard residential HVAC systems. Requires a dedicated HEPA bypass filtration unit.

Whole-Home Air Purification Options

UV germicidal lights ($500-$1,500 installed): Mounted inside the ductwork near the evaporator coil, UV-C lights kill mold, bacteria, and viruses as air passes through. They don't filter particles but neutralize biological contaminants. Especially valuable in humid climates where mold growth inside ductwork is common. Maintenance: replace the UV bulb annually ($50-$100).

Electronic air cleaners ($800-$2,000 installed): Use electrical charges to capture particles as air passes through. More effective than standard filters without the airflow restriction of high-MERV filters. Maintenance: clean the collection plates every 1-3 months.

Whole-home HEPA filtration ($1,500-$3,000 installed): A bypass HEPA filter unit installed in the ductwork that filters a portion of your home's air continuously. Doesn't restrict main airflow because it operates as a secondary filtration loop. The gold standard for residential air purification.

Humidity Control

Proper humidity is critical for both health and comfort. The ideal indoor range is 30-50% relative humidity. Too high (above 50%): Promotes mold growth, dust mites, and bacterial proliferation. Makes warm temperatures feel warmer. Solutions include whole-home dehumidifiers ($1,500-$2,500 installed) and properly sized AC (which dehumidifies as it cools). Too low (below 30%): Causes dry skin, respiratory irritation, and static electricity. Common in winter when heated air is very dry. Solutions include whole-home humidifiers ($400-$1,000 installed) that add moisture to the airstream.

Duct Cleaning: Necessary or Scam?

Professional duct cleaning is one of the most debated topics in HVAC. The EPA's official position is that duct cleaning has not been shown to prevent health problems in the absence of visible contamination. When duct cleaning IS worth it: visible mold growth inside ducts, rodent or insect infestation in ductwork, significant dust or debris buildup visible inside ducts, and after major home renovations that generated construction dust. When it's NOT necessary: as routine maintenance on clean systems, when sold as a "health improvement" without visible contamination, or as part of a high-pressure upselling package from an HVAC company. If you do get ducts cleaned, use an NADCA-certified contractor and expect to pay $300-$700 for a thorough job. Beware of $99 "whole-house specials" - they're usually bait-and-switch operations.