Indoor air quality
The air inside your home is typically 2 to 5 times more polluted than outdoor air. Here is what is in it and how to improve it.
The problem
The US EPA ranks indoor air quality as one of the top five environmental health risks. Most people spend over 90% of their time indoors, making indoor air quality a more significant daily exposure than outdoor air for the majority of people.
The main sources of indoor air pollution: building materials and furniture off-gassing VOCs, cleaning products and air fresheners, cooking particulates and combustion byproducts, HVAC systems distributing mould spores and particles, and outdoor air infiltration. Homes that are well-sealed for energy efficiency can have particularly poor air quality without adequate ventilation.
Key indoor air pollutants
VOCs (volatile organic compounds)
Paint, furniture, flooring, cleaning products
Particulate matter (PM2.5)
Cooking, candles, dust, incense
Formaldehyde
New furniture, pressed wood, MDF, flooring adhesives
Mould spores
Moisture, HVAC systems, poorly ventilated bathrooms
Carbon monoxide
Gas appliances, boilers, wood burning stoves
Radon
Geological source. Varies significantly by region. Seeps through foundations.
Sources you might not expect
Scented paraffin candles
Burn paraffin wax (a petroleum product) and release VOCs and fine particulates. Soot from candles can be detected on walls and ceilings over time. Use beeswax or soy candles with essential oil fragrance instead.
Air fresheners
Most plug-in and spray air fresheners contain VOCs and synthetic fragrance. They mask odours by adding more chemicals. They do not remove pollution from air. They are a net negative for indoor air quality.
New furniture off-gassing
Pressed wood furniture (MDF, particleboard) and foam-filled sofas can off-gas formaldehyde and VOCs for months to years after manufacture. A new sofa can take 6 months to 2 years for formaldehyde levels to dissipate meaningfully.
Synthetic carpet
Traps and re-releases VOCs. Acts as a reservoir for dust-bound toxins. Wall-to-wall carpet in a living space is a persistent background source of chemical exposure.
Non-stick cookware above 260 degrees C
PTFE (Teflon) coatings begin to degrade above 260 degrees C and release fluoropolymer particles and gases. Fatal to pet birds. Potentially harmful to humans at high temperatures. Use cast iron, stainless steel or ceramic-coated alternatives.
Ventilation first
Opening windows is free and the most effective single action for reducing indoor air pollutant concentrations. Cross-ventilation, created by opening windows on opposite sides of the home, is significantly more effective than opening windows on one side only.
When to ventilate:
- During and after cooking (particulates, combustion gases)
- After cleaning with any conventional products
- During the first weeks after receiving new furniture
- During and after painting
- When CO2 levels feel elevated (stuffiness, difficulty concentrating)
Air purifier guide
There are two distinct filtration technologies that address different types of pollution:
HEPA filtration
Removes particles down to 0.3 microns: PM2.5, mould spores, dust, pollen, pet dander. Does NOT remove gases or VOCs.
Activated carbon
Adsorbs VOCs, gases, odours and formaldehyde. Does NOT remove particles. Both are needed for comprehensive coverage.
What about plants?
The famous NASA Clean Air Study (1989) found that certain plants removed VOCs from sealed test chambers. However, the study was conducted in small, sealed, low-ventilation chambers with VOC concentrations far higher than typical homes. Subsequent analysis has found that you would need over 10 plants per square metre of floor space to achieve meaningful VOC reduction in a real home with normal air exchange.
Practical benefit of plants: marginal for VOC removal, moderate for humidity regulation in dry environments, and significant psychological benefit. They are worth having, but they are not a substitute for ventilation or filtration.
Best-studied plants: spider plant (Chlorophytum comosum), peace lily (Spathiphyllum), snake plant (Sansevieria). Note: peace lily and many common houseplants are toxic to cats and dogs.
"The concentrations of many VOCs are consistently higher indoors than outdoors, regardless of whether the building is located in rural or highly industrial areas."
US Environmental Protection Agency – epa.gov/indoor-air-quality-iaq
Do not panic
The order of priority is: ventilate first, remove sources second, filter third. An air purifier in a poorly ventilated room full of off-gassing furniture will struggle. Opening windows costs nothing and makes the biggest difference immediately.
Priority actions
More polluted than outdoor air. The US EPA identifies indoor air quality as one of the top five environmental health risks.
Air purifier recommendations
Coway Airmega 400
Best value for most homes. Covers up to 360 sq ft. Dual filtration.
View productIQAir HealthPro Plus
Medical-grade HyperHEPA filtration. Best performance available. Hospital and clinic grade.
View productDyson Purifier Hot+Cool
Good performance with app integration. Carbon filter depth limited compared to IQAir. High price relative to performance.
View productLevoit Core 300
Budget option. HEPA filtration for particles. Limited carbon filter: inadequate for VOC removal. Best for bedrooms with particle concerns only.
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