Winter Heating and London's Air

Winter is quietly one of the worst seasons for London indoor air. Wood-burning stoves and open fires are a major and growing source of PM2.5 — a single evening's burning can raise particulate levels sharply, indoors and out. Add sealed-up, less-ventilated rooms and cooking, and winter indoor air often beats summer for particle counts.

The winter sources

• Wood burners & open fires — the big one for PM2.5.
• Gas cooking & heating — NO2 indoors.
• Reduced ventilation — pollutants build up with windows shut.

Staying warm and clean

If you burn wood, run a high-airflow purifier in the same room while the stove is lit and after. Ventilate briefly when cooking. A MERV-13 kit clears the particulates; add carbon for smoke odour.

Why London's winter air turns inward

For most of the year Londoners think of pollution as something outdoors — the exhaust on Marylebone Road, the haze over the South Circular. In winter the problem quietly moves inside. Two things happen at once. Wood burning climbs steeply from November through February, and it has become one of the fastest-growing residential sources of PM2.5 in the capital; even a single evening's fire in a terraced street can lift particle levels across neighbouring gardens and back into open windows. At the same time, we seal the house against the cold, so whatever is generated indoors — from the stove, the gas hob, candles or cooking — has nowhere to go and simply accumulates.

The result is that a cosy London front room on a still January night can carry a higher particle count than the street outside, which runs against most people's instinct. Cold, calm, high-pressure spells make it worse still, trapping a shallow layer of air over the city so that wood smoke lingers rather than dispersing. The London Air Quality Network regularly logs these winter particle peaks, and they line up closely with cold snaps and the evening burning window.

Staying warm without breathing the smoke

You do not have to choose between a warm home and clean air, but you do need to manage the burning actively. The single most effective move is to run a high-airflow purifier in the same room as the stove or fire — both while it is lit and for an hour or two afterwards, when the finest particles are still suspended. Because wood smoke is both particulate and odour, a unit with an activated-carbon stage handles the smell that a plain particle filter leaves behind.

• A MERV-13 filter captures roughly 93% of fine particles; the trade-offs against true HEPA are set out in MERV-13 versus HEPA.
• To build your own high-airflow box cheaply, see the Corsi-Rosenthal box UK guide.
• Winter heating also drives up damp and mould in London's older, colder flats — our air purifier for mould page covers that side of the season.
• Households with asthma feel wood smoke most sharply; see air purifier for asthma.

Add short bursts of ventilation while cooking, keep the flue and stove well maintained, and the winter particle spike becomes a manageable problem rather than an invisible one.