Indoor air is often worse than outdoor, here's what to do

What's in there with you

CO₂. Builds up when you sleep, work, or have people round. Over 1000ppm makes you sluggish. Over 1500ppm, decision-making and focus measurably drop.

VOCs. Volatile organic compounds from cleaning products, candles, air fresheners, paint, new furniture glue, vinyl floors, even dry-cleaned clothes.

PM2.5. Mostly from cooking on gas, vacuuming without a HEPA, candles, fireplaces, incense.

Formaldehyde. Off-gasses from new furniture, plywood, insulation. Worst in the first two years.

Mould spores. Anywhere humidity sits above 65% for hours.

Five things that fix most of it

1. Open the windows daily

Ten to fifteen minutes in the morning and again in the evening flushes out the CO₂ and VOCs. Skip on high-AQI days outside.

2. Always use the kitchen extractor

Especially on gas. Gas stoves emit NO₂, CO, and PM2.5 you can't see or smell.

3. HEPA purifier in the bedroom

You spend a third of your life there. HEPA plus carbon. Run it on low overnight.

4. Shoes off at the door

Shoes track in lead, pesticides, fungal spores, pollen. House dust drops by 60% with a no-shoes rule.

5. Houseplants are mostly symbolic

The famous NASA clean-air study is misunderstood. You'd need 100+ plants to measurably improve air quality in an average room. Plants are great for mood. Ventilation and filtration are what actually clean the air.

The most underrated gadget

A CO₂ monitor. Eighty dollars, lasts years, shows you exactly when the bedroom needs airing out. Most people are shocked at their numbers in the morning, often over 2000ppm.

The pollutants hiding in a normal home

Indoor air routinely tests worse than the air outside, and the sources are ordinary household activity. Cooking, especially frying and gas hobs, throws out fine particles and nitrogen dioxide. Cleaning products, paints, air fresheners, and new furniture release volatile organic compounds. Damp corners grow mould spores. Add in dust, pet dander, and the carbon dioxide we all exhale in a closed room, and a sealed modern home can accumulate a surprising load. Because we spend the great majority of our time indoors, this is the air that matters most for our health.

Ventilation is the cheapest fix

The simplest, cheapest improvement is fresh air. Opening windows on opposite sides of the home for even ten minutes creates a cross-breeze that flushes out stale, pollutant-laden air and replaces it. Do this after cooking, after showering, and first thing in the morning. The one time to be cautious is when outdoor air quality is genuinely poor, during bushfire smoke or a high-pollution day, when you are better off keeping windows shut and running a purifier instead. Checking the local air quality index tells you which situation you are in.

Extractor fans, purifiers, and plants

Use the extractor fan every single time you cook or shower; these are the two biggest moisture and particle events in a normal day, and the fan removes the problem at the source. A HEPA air purifier sized to the room is worthwhile if anyone has asthma or allergies, or if you live somewhere with frequent poor outdoor air. Houseplants get talked up for air cleaning, but the honest truth is you would need a small forest to match what ten minutes of open windows achieves; enjoy them for how they look, not as an air-quality strategy.

Frequently asked questions

Is indoor air really worse than outdoor air?

Often, yes. Studies regularly find indoor concentrations of several common pollutants higher than outdoors, because everyday activities release them and a closed home lets them build up. Ventilation is what keeps them in check.

Do houseplants clean the air?

Barely, in real-world amounts. The famous experiments used sealed lab chambers. In a normal room you would need an impractical number of plants to make a measurable difference. Open windows and an extractor fan do far more.

When should I keep windows closed instead of open?

When outdoor air quality is poor, such as during bushfire smoke, heavy traffic pollution, or a high-pollen morning. On those days, keep windows shut and rely on a purifier, then air the home when conditions improve.

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