How to Improve Indoor Air Quality at Home

People in many industrialised countries spend roughly 90 percent of their time indoors, and a large share of that time is at home. Because homes are relatively enclosed compared to outdoor spaces, pollutants generated inside, from cooking, cleaning, combustion and moisture, can build up to concentrations that wouldn't occur outdoors, and in some cases indoor concentrations of certain pollutants can exceed typical outdoor levels.

This doesn't mean every home has a serious air quality problem. It means air quality is worth paying attention to as a routine part of home maintenance, similar to checking smoke detectors or servicing an HVAC system, rather than something to worry about only when there's an obvious sign like a smell or visible mould.

The most effective starting point isn't buying equipment, it's figuring out what's actually generating pollutants in your specific home. Common sources include gas stoves and combustion appliances (CO2, PM2.5, formaldehyde-related VOCs), cooking generally (PM2.5, PM10), cleaning products, air fresheners and personal care products (VOCs), new furniture, flooring or paint (formaldehyde and other VOCs, especially when new), and damp areas like bathrooms, basements and kitchens (moisture, mould risk).

A common mistake is assuming outdoor pollution is the main concern and overlooking indoor sources entirely; in reality, everyday indoor activities like cooking and cleaning are often bigger contributors to what you actually breathe than infiltration from outside. Walking through the home room by room and noting likely sources, rather than guessing, is the most reliable way to prioritise.

Ventilation dilutes indoor pollutants with outdoor air and is one of the most effective tools available, particularly for CO2 and general VOC build-up. ASHRAE Standard 62.2, the primary US reference for residential ventilation, recommends a baseline whole-house rate of roughly 7.5 cfm per occupant plus 0.03 cfm per square foot of floor area, achieved through some mix of natural infiltration, operable windows, and mechanical systems like exhaust fans or a whole-house ventilation system.

Filtration removes particles from air already inside the room rather than replacing it, which makes it a useful complement to ventilation, especially when outdoor air isn't suitable to bring in. HVAC filters are rated by MERV (Minimum Efficiency Reporting Value) on a scale that generally runs from 1 to 16, with higher numbers capturing smaller particles more effectively; the EPA notes that filters rated MERV 13 or above are required to demonstrate at least 50 percent removal efficiency for the smallest particles tested, making MERV 13 a commonly recommended minimum for meaningful particle control.

HEPA filters, commonly used in portable air purifiers, are a separate standard defined by performance rather than the MERV scale: a true HEPA filter captures at least 99.97 percent of particles at the hardest-to-capture 0.3 micrometre size, which the EPA notes roughly corresponds to MERV 16. When choosing a portable air purifier, the EPA recommends checking its Clean Air Delivery Rate (CADR), which measures how much clean air it produces per minute, and sizing it to the room rather than assuming a purifier is effective regardless of room size.

Humidity affects comfort, mould risk and dust mite populations, and it interacts with ventilation and filtration rather than operating independently. Too little humidity dries out airways and skin; too much supports mould growth and dust mite proliferation, particularly above roughly 60 to 70 percent.

Volatile organic compounds come from a wide range of everyday products: paints, adhesives, cleaning products, air fresheners, scented candles, new furniture and flooring, and personal care products. VOC levels are typically highest when a product is new or freshly applied, then decline over time, which is why ventilating well after painting, installing new flooring, or bringing home new furniture is particularly important.

Source control is generally the most effective approach: choosing low-VOC or fragrance-free products where practical, storing chemicals in a ventilated space like a garage rather than a closet, and airing out new furniture before it goes into a bedroom. Ventilation and, to a lesser extent, activated-carbon filtration can help with what's already in the air, but they work best alongside source control rather than as a replacement for it.

Because pollutant levels shift throughout the day, cooking raises PM2.5, a full house raises CO2, cleaning raises VOCs, a single measurement taken once tells you very little about what's actually typical in a home. Continuous monitoring of PM2.5, CO2, TVOCs, temperature and humidity makes it possible to see which rooms, activities or times of day drive the biggest changes, and to check whether a change you've made, like adding a purifier or adjusting ventilation, actually worked.

Monitoring is most useful as a feedback tool rather than a one-time diagnosis: identify a pattern, make a targeted change, and check whether the readings improve. This also helps avoid the common mistake of treating every fluctuation as a crisis; some rise in PM2.5 during cooking or CO2 in a full room is normal, and what matters more is the overall pattern and how quickly levels return to baseline.