How do I improve air quality indoors?
Ventilation before purification, the sources worth removing, and where an air purifier genuinely helps and where it does not.
- Difficulty
- beginner
- Time
- 45 min
- Read
- 5 min
- Safety
- caution
Short answer
Ventilation is the answer to most of it — extract at the source when cooking and showering, and open windows briefly and widely rather than slightly all day. Remove sources where you can. A purifier helps with particles but does nothing for moisture or CO2.
Indoor air is usually worse than outdoor air, and the reasons are mundane: cooking, moisture, cleaning products and a house sealed up to save heat.
Safety
What you'll need
- Working extractor fans in kitchen and bathroom
- A carbon monoxide alarm
- Optionally, a cheap CO2 or humidity monitor
Step by step
- Ventilate properly rather than constantly.Windows wide open for five to ten minutes exchanges the air with far less heat loss than a window on the latch all day. Do it a couple of times daily, and after cooking or showering.
- Use the extractor at the source.Kitchen and bathroom fans, switched on before you start and left running for fifteen minutes afterwards. Capturing moisture and fumes where they are produced beats diluting them later.
- Check the extractors actually work.Hold a sheet of tissue against the grille — it should hold there. Many fans run without moving meaningful air because the ducting is blocked, crushed or disconnected in the loft.
- Cook with the lid on and the fan running.Gas hobs produce nitrogen dioxide, and frying produces fine particles. Cooking is the largest single source of indoor particulate in most homes, and extraction at the hob addresses it.
- Control moisture.Damp air carries mould spores and dust mites. Dry washing outside where possible, cover pans, and keep relative humidity roughly between 40 and 60 percent.
- Never block permanent vents.Air bricks and wall vents serving a boiler, fire or stove are there to prevent carbon monoxide. Blocking them to stop a draught is dangerous.
- Reduce what you put into the air.Aerosols, strong solvent cleaners, air fresheners and scented candles all add volatile compounds. Fewer products and simpler ones make a measurable difference.
- Ventilate when using anything strong.Paint, adhesives, oven cleaner, new furniture off-gassing. Windows open during and for a good while afterwards.
- Deal with mould rather than covering it.Visible mould releases spores continuously. Remove it, then fix the moisture that caused it, or it returns within weeks.
- Vacuum with a HEPA filter.An ordinary vacuum can put fine dust straight back into the room. A sealed HEPA machine, used regularly, genuinely reduces airborne particles.
- Take shoes off at the door.It keeps out a surprising amount of outdoor particulate, and it is free.
- Be realistic about houseplants.The famous research was done in sealed laboratory chambers. At household scale the effect is negligible — you would need an impractical number. Keep them because you like them.
- Use a purifier for the right problem.A HEPA purifier is effective on fine particles, pollen and smoke, which helps for allergies. It does nothing for moisture, CO2 or most gases unless it has a substantial carbon filter.
- Size and place a purifier properly.Match the rated room size, run it continuously on low rather than briefly on high, and keep it away from walls and furniture. Change the filters as specified.
- Avoid ozone generators and ionisers.Ozone is a respiratory irritant and generators are not recommended for occupied spaces. Filtration is the safe approach.
- Consider a monitor if you want to know.An inexpensive CO2 and humidity monitor tells you when a room actually needs ventilating rather than guessing. CO2 above about 1000ppm is a good prompt to open a window.
Tips
- Windows wide for ten minutes beats a window ajar all day, and loses far less heat.
- Tissue test your extractor fans. Many run without moving any real air.
- Houseplants do not clean indoor air at household scale. Ventilation does.
Common mistakes
- Blocking air vents to stop draughts — Vents serving a boiler, fire or stove supply the air for combustion. Blocking them risks carbon monoxide, which is colourless, odourless and fatal.
- Buying a purifier instead of ventilating — A purifier filters particles but does nothing about moisture, CO2 or most gases. If the underlying problem is a sealed house with no extraction, it treats a symptom.
If it doesn't work
Stuffy, stale air
Cause: Insufficient air exchange — Fix: Open windows wide for ten minutes twice a day. A CO2 monitor tells you when it is needed.
Condensation and mould
Cause: Too much moisture, too little ventilation — Fix: Extract at source when cooking and showering, dry washing outdoors, and remove existing mould before it spreads.
Extractor running but the mirror still steams
Cause: Blocked or disconnected ducting — Fix: Tissue test it, then check the duct run and the external grille for blockage or a crushed flexible hose.
Allergy symptoms worse indoors
Cause: Dust, pollen or pet dander — Fix: HEPA vacuum regularly, wash bedding hot, and consider a HEPA purifier in the bedroom.
Cooking smells lingering for hours
Cause: Recirculating hood rather than extracting — Fix: Check whether the hood vents outside or filters and recirculates. A recirculating hood needs its carbon filter changed regularly.
Questions people ask
Do air purifiers actually work?
For fine particles, pollen and smoke, a properly sized HEPA unit works well. They do not address moisture, CO2 or most gases, and they are no substitute for ventilation.
Do houseplants clean the air?
Not meaningfully at household scale. The often-quoted study used sealed chambers; you would need many plants per room to match opening a window for a few minutes.
How often should I open the windows in winter?
Briefly and widely — five to ten minutes, twice a day, plus after cooking and showering. Short bursts exchange the air without cooling the walls and furniture.
Is a gas hob bad for indoor air?
It produces nitrogen dioxide and fine particles while in use. Extraction that vents outside, used every time you cook, is the practical answer rather than replacing the hob.