The Air we share: Why indoor air quality matters for our health
Paul Kershaw, of SOW and Cambridge Retrofit Hub, gave a talk on 11th February 2026 about Indoor Air Quality. The slides are here but below are some extra notes from the talk.
The examples of the Clean Air Act 1952 and of the transformations in Beijing (factories shut down for the Olympics) and New Delhi (lockdown) show that we can clean outside air outside, so cleaning it inside our homes ought to be achievable.
Be wary that different thermostats can record slightly different temperatures, so don’t get hung up on the exact values. The important point is not to go too low.
Most damp and mould is as a result of fuel poverty.
Humidity is an effective indication of ventilation in the home. Humidity monitors are cheaper than air quality monitors.
Any home with gas heating or cooking should have a CO detector.
Recommend turning cooker hoods on 5 minutes before cooking and keep running for 5 minutes afterwards, similarly bathroom fans should be kept on for 5 minutes after the room has been left.
Paul’s top tip was “purge ventilation“, also known as Stoßlüften (shock ventilation) or “house burping” – see the slides (slide 25) for instructions. It’s about replacing the air without taking the heat out of the house. If you live on a main road, don’t do it in rush hour, and in summer, not when it’s hottest outside.
Trickle vents in windows were introduced because people don’t tend to do purge ventilation,but they are not great for heat loss and Paul recommended not leaving them open all day but purge ventilating instead. At night they can be useful if you can’t sleep with the bedroom door open. If you wake with a headache it could be due to too much CO2 in the room from lack of ventilation.
Wood burning stoves now cause more than 2.5 as much pollution as vehicles. The occasional log fire is OK but they are not healthy, and woodburners should be sold with a health warning.
We have a lot more moisture in our houses now than in previous generations. We wash and bathe a lot more than people used to so old houses that were OK in the past now get damp. Drying clothes on radiators is not good, better is on a clothes horse in a room with an extractor fan.
Extractor fans often aren’t big enough – builders won’t have calculated how much air needs to be extracted.
Mechanical ventilation with heat recovery is the gold standard for ventilating houses, but it’s expensive/disruptive to retrofit. It does cause some heat to be lost from the home (10%).
During the course of the talk we recorded the effect of ten people sitting in the room together!
Sustainable Oakington and Westwick 