How do I improve indoor air quality at home?

What this usually means

Indoor air quality describes how clean, fresh and healthy the air in your home is, and it is determined by a balance between the pollutants being added and the rate at which ventilation removes them. The main things to manage are carbon dioxide from occupants, water vapour from daily activities, fine particles from cooking and outdoor air, and volatile organic compounds from furnishings, cleaning products and combustion. Improving air quality means reducing these at source where possible and ventilating to clear the rest.

This is why ventilation is the foundation of good air quality rather than an optional extra. No matter how clean you keep the home, occupants will always produce carbon dioxide and moisture, cooking will always release particles and vapour, and materials will always off-gas some compounds. Only a steady supply of fresh air and removal of stale air keeps these at healthy levels. Air purifiers can help with particles, but they do not remove carbon dioxide or moisture and cannot replace ventilation.

The reason to measure rather than guess is that each pollutant has a different source and remedy, and you cannot smell or see most of them. Carbon dioxide signals ventilation adequacy; humidity signals moisture balance and mould risk; PM2.5 signals particle sources and filtration needs; VOCs signal off-gassing and combustion. Measuring them shows which are actually elevated in your home, so the improvements — more ventilation, better extract, source control, filtration — are targeted at the real problem.

Common causes

Signs and symptoms

Indoor air quality is governed by the same mass-balance principle as stuffiness: the concentration of any pollutant settles where its production rate equals its removal rate. Removal happens through ventilation (for gases and vapour) and, for particles, additionally through filtration and settling. So for carbon dioxide and water vapour, ventilation is the only practical control — there is no filter that removes them — while for particles, both ventilation and filtration play a part. Understanding which mechanism removes which pollutant is what makes an air-quality strategy effective rather than hopeful.

Humidity deserves particular attention because it links air quality to the building itself. High relative humidity not only feels unpleasant and supports dust mites; it also raises the surface humidity on cold surfaces, driving condensation and mould that further degrade the air and damage the fabric. Controlling moisture — through source extract and ventilation — therefore improves both the air and the durability of the home, which is why it sits at the centre of a building-physics approach.

Source control is the most efficient lever because it reduces the production side of the balance. Extracting cooking particles and moisture at the hob, choosing low-emission materials and products, and avoiding indoor laundry drying all lower the load that ventilation has to remove. Combined with ventilation that is sized and balanced — ideally filtered MVHR in tighter homes, which supplies fresh outdoor air while filtering incoming particles and recovering heat — this delivers consistently good air quality. Measuring carbon dioxide, humidity, PM2.5 and VOCs first ensures the effort is directed at whichever of these is genuinely elevated.

How to improve indoor air quality, step by step

Work from measurement to source control to ventilation, targeting whichever pollutants are actually elevated. This delivers real improvement rather than masking symptoms.

1. 01

   Measure what's actually in the air

   Log carbon dioxide, humidity, PM2.5 and (where relevant) VOCs to see which pollutants are elevated and where.

2. 02

   Control pollutants at source

   Extract cooking particles and moisture at the hob, avoid indoor laundry drying, and reduce VOC-heavy products and fresheners.

3. 03

   Provide adequate ventilation

   Ensure background and extract ventilation, and consider balanced filtered MVHR in tighter homes for continuous, efficient fresh air.

4. 04

   Manage humidity

   Keep relative humidity in a healthy range through ventilation and source control, preventing condensation and mould.

5. 05

   Add filtration where particles are the issue

   Use filtered mechanical ventilation or a purifier to address fine particles — as a supplement to ventilation, not a replacement.

6. 06

   Re-measure to confirm

   Check that carbon dioxide, humidity and particles now sit in healthy ranges through normal use, proving the improvements worked.

How to prevent it coming back

• Extract cooking and bathroom moisture and particles at source, every time.
• Keep relative humidity moderate through ventilation rather than letting it build up.
• Choose low-emission materials and limit VOC-heavy products indoors.
• Provide controlled, ideally filtered, ventilation — especially in airtight homes.
• Monitor air quality so problems are caught and corrected early.