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To improve indoor air quality, work in the order the EPA gives: remove or reduce the sources of pollution first, ventilate with fans that exhaust outdoors and with open windows when weather allows, and only then filter with the best HVAC filter the system can handle and, if needed, a portable air cleaner sized to the room. Two gases, radon and carbon monoxide, need a test and an alarm rather than a filter. Everything else on this list is a habit, a fan, or a filter change.
What improves indoor air quality the most?
Source control improves indoor air the most, then ventilation, then filtration. The EPA's page on improving indoor air quality says the most effective way is usually to eliminate individual sources of pollution or reduce their emissions, and that source control is more cost-efficient than increasing ventilation. Ventilation dilutes what is left. Filtration catches particles and little else.
The EPA's guide to air cleaners in the home puts it directly: "Filtration does not replace the need to control pollutants and ventilate," and "No air cleaner or filter will eliminate all of the air pollutants in your home."
Which sources should you remove or reduce first?
Start with combustion, solvents, and moisture, because they produce the pollutants that filters cannot catch; then dust and dander, which filters can. The EPA's page on volatile organic compounds says concentrations of many VOCs are consistently higher indoors, up to ten times higher, than outdoors, and names paints, varnishes, cleaning products, degreasers, and hobby supplies as sources, along with building materials and furnishings.
| Source | What it puts in the air | What to do |
|---|---|---|
| Gas range, fuel-burning heaters, fireplaces | Combustion gases, particles | Run a range hood vented outdoors; keep fuel appliances serviced; CO alarms near sleeping areas |
| Paints, solvents, adhesives, cleaners | VOCs | Use outdoors or with windows open; buy only what you will use; store sealed in the garage or shed, not a closet |
| Damp bathrooms, basements, crawl spaces | Mold spores, musty odor | Fans vented outdoors, fix leaks, hold humidity below the EPA's numbers |
| Attached garage | Exhaust, fuel vapors | Never idle a car inside; keep the door to the house weatherstripped and closed |
| Carpet, bedding, pets | Dust, dander, allergens | Vacuum with a sealed or HEPA machine; wash bedding hot; a good HVAC filter |
| Dryer vented indoors or into a wall | Lint, moisture | Check the dryer vent reaches outdoors and is clear |
The EPA's VOC page also says to increase ventilation when using products that emit them and to throw away unused containers safely rather than storing them. A can of half-used stain in a hall closet is a source that runs all year. If mold is the source, what to do when you find it covers the size rule and the cleanup.
How much ventilation does a house need?
A house needs enough ventilation to carry moisture, cooking, and bathroom air outdoors as it is made, and to dilute the rest. The EPA's improving-air-quality page says bathroom and kitchen fans that exhaust outdoors remove contaminants directly from the room, that opening windows or running window and attic fans raises the ventilation rate, and that you should ventilate most during short-term activities such as painting, cooking, sanding, or soldering.
The catch is the word outdoors. A bath fan that dumps into the attic, or a recirculating range hood, moves the air around without removing anything. Cleaning the bathroom exhaust fan and checking that it vents outside is a one-time attic look plus a tissue test. ENERGY STAR's windows page adds the habit: use the fans during showers and cooking and leave them running for 20 minutes afterward.
The ventilation habits that do the work
- Run the bath fan during every shower and 20 minutes after; a timer switch makes it automatic
- Run the range hood whenever a burner is on, especially on a gas range
- Ventilate hard, or work outdoors, when painting, stripping, sanding, or gluing
- Confirm once that every exhaust fan and the dryer terminate outdoors, not in the attic or a wall
- If the house has a fresh-air system, ERV, or HRV, confirm it is switched on and its filter is clean
A newly built home is tight enough that it depends on its mechanical ventilation running, and it holds construction moisture and new-material off-gassing for the first year. Indoor air quality in a tight new home covers the fresh-air system, the first-year moisture, and what to ask the builder.
Which filter and air cleaner should you use?
Use the highest-rated HVAC filter the system can handle, changed on schedule, and add a portable air cleaner only for a room with a particle problem, sized by its CADR. The EPA's MERV page explains that MERV reports a filter's ability to capture particles between 0.3 and 10 microns and suggests at least a MERV 13 rating, or as high a rating as your system fan and filter slot can accommodate, checked with an HVAC technician.
The Building America Solution Center's filter guide adds the caution: higher MERV filters can clog faster and restrict airflow, so check with the HVAC service company before jumping to MERV 13 or higher. Replacing the HVAC filter covers the size, the arrow direction, and the monthly check. A clogged MERV 13 is worse for the blower than a clean MERV 8.
For a portable air cleaner, the EPA's air cleaner guide says the higher the CADR, the more particles it can filter and the larger the area it can serve, and gives a sizing table:
| Room area (square feet) | Minimum CADR (cfm) |
|---|---|
| 100 | 65 |
| 200 | 130 |
| 300 | 195 |
| 400 | 260 |
| 500 | 325 |
| 600 | 390 |
The same guide warns that ozone generators sold as air cleaners intentionally produce ozone, a lung irritant, and that portable air cleaners and HVAC filters do not address the cause of mold and musty odors.
In Property Station the filter is a recurring task on the Maintenance page with a frequency in months and a reminder a week before it is due; the filter size and MERV rating go on the HVAC system's page so the next purchase is a lookup, not a guess. See how the scheduler works.
What about the invisible gases: radon and carbon monoxide?
Radon and carbon monoxide need a test and an alarm, not a filter. The EPA's air cleaner guide says it does not recommend air cleaners to reduce radon; the only way to know a home's radon level is to test it. Carbon monoxide comes from anything that burns fuel, including a car in an attached garage, and the defense is a working alarm near every sleeping area plus yearly service on fuel-burning equipment.
Testing your home for radon covers the kit, the placement, and what the EPA action level means. Testing smoke and CO detectors covers the monthly button press and the replacement dates.
Common questions
What is the fastest way to improve indoor air quality?
Remove or reduce the source. The EPA says eliminating individual sources of pollution is usually the most effective step and costs less than adding ventilation. Vent the range hood and bath fans outdoors, keep solvent products out of living space, and fix moisture. Then check the HVAC filter.
Do air purifiers actually work?
Some do, for particles. The EPA says some air cleaners are highly effective at removing particles while most table-top models are much less so, and that air cleaners are generally not designed to remove gases. Size one by its CADR against the room, and skip ozone generators; ozone is a lung irritant.
Is MERV 13 too much for my furnace?
Maybe. The EPA suggests at least MERV 13, or as high a rating as your fan and filter slot can accommodate. Higher-rated filters restrict airflow more, so a system with a thin one-inch slot or a weak blower may struggle. Ask the HVAC technician at the next tune-up, and change whatever you use on schedule.
What should you do next?
Walk the house once with the source table in hand and move, seal, or vent whatever you find. Then check the filter, run the tissue test on every exhaust fan, and put the filter change on a recurring schedule. If the house feels damp or the windows sweat, the humidity numbers and fixes are the next read; if the ducts are on your mind, when duct cleaning is justified will probably save you the call.