Air Quality
Indoor Air Quality Guide
Quick answer
Indoor air is typically 2 to 5 times more polluted than outdoor air. The effective strategy is layered: source control first, then ventilation to dilute, then MERV 11 to 13 filtration to capture particles, then targeted extras like ERVs and portable HEPA units. Duct cleaning and ionizers rank last for good reasons.
Know your enemy: the pollutants that matter
Different pollutants need different weapons, which is why no single device fixes air quality.
- Particulates (PM2.5): smoke, dust, dander, pollen; the best studied health risk, addressed by filtration
- Biological: mold spores, dust mites, bacteria, viruses; addressed by humidity control plus filtration
- VOCs: off gassing from paints, furniture, cleaners; filtration barely touches them, ventilation and source removal work
- Combustion products: CO, NO2 from gas stoves, furnaces, attached garages; addressed by venting, sealing, and detectors
- Radon: the second leading cause of lung cancer, entering through foundations; addressed only by testing and mitigation, never by air cleaners
Upgrades ranked by real payoff
Ordered by evidence and cost effectiveness, not by marketing volume.
Source control (nearly free)
Run range hoods vented outside, ban indoor smoking, choose low VOC products, fix moisture problems, keep garage doors to the house sealed.
Filter upgrade ($20 to $700)
MERV 11 to 13, ideally in a 4 to 5 inch media cabinet. This is the highest value hardware step for particles.
Humidity control ($0 to $2,800)
Hold 30 to 50 percent. Kills the dust mite and mold pathways at the root.
Ventilation ($400 to $4,500)
Bath and kitchen exhaust working properly, then an ERV or HRV in tight homes to bring in filtered fresh air without losing conditioning.
Portable HEPA units ($100 to $700 per room)
Genuinely effective for bedrooms, wildfire smoke events, and allergy sufferers; look for adequate CADR for the room size.
UV coil lights ($300 to $800)
Legitimate for keeping the AC coil biofilm free in humid climates; modest effect on the air itself.
What to skip and why
Duct cleaning is rarely worth it: EPA guidance finds no demonstrated health benefit from routine cleaning, and it earns its fee only for visible mold in ducts, vermin infestation, or post construction debris. Ionizers and some electronic air cleaners generate ozone, a lung irritant, while consumer plug in purifiers without HEPA filtration move air without cleaning it, and scent products add VOCs while masking odors. Spend that money on the ranked list above, and if anyone recommends duct cleaning to fix odors, find the odor's source instead.
Frequently asked questions
Does duct cleaning improve air quality?
Rarely. The EPA does not recommend routine duct cleaning, finding no demonstrated health benefit, because dust adhered inside ducts mostly stays there. Legitimate triggers are visible mold growth, vermin, or construction debris. Persistent dust and odors usually trace to filtration, leaks, or humidity instead.
What helps with wildfire smoke indoors?
Close up the house, run the HVAC fan continuously with the best filter your system tolerates, MERV 13 where possible, add portable HEPA units in occupied rooms, and avoid activities that add particles like frying and candles. A media cabinet upgrade before fire season is the durable fix in smoke prone regions.
Are gas stoves really an air quality problem?
They emit NO2 and fine particles at levels that regularly exceed outdoor standards in kitchens without ventilation. The fix is behavioral and cheap: use a range hood vented outdoors every time you cook, or crack a window when you lack one. Induction eliminates the source for those replacing anyway.
Related guides
- Best HVAC Filters: MERV Ratings ExplainedHow to choose HVAC filters by MERV rating, why higher is not always better, filter types compared, and replacement schedules that protect your system.
- Indoor Humidity GuideThe ideal indoor humidity range, how to fix a home that is too damp or too dry, and how HVAC equipment controls moisture.
- HVAC Maintenance ChecklistThe complete homeowner HVAC maintenance schedule: monthly, seasonal, and annual tasks that extend equipment life and cut energy bills.
- HVAC Energy Saving GuideThe HVAC energy savings hierarchy: no cost habits, low cost fixes, and equipment upgrades ranked by return, with realistic percentage savings for each.