Four fire engines and around 25 firefighters were called to a flat fire on Cassandra Close in Northolt.
Most of a flat on the first floor of a two-storey block was damaged by the fire. A small part of the first floor communal hallway and a small part of a neighbouring flat were also damaged.
One man left the affected flat before the Brigade arrived. He was taken to hospital by London Ambulance Service (LAS) crews suffering smoke inhalation.
Another four people left the building before the Brigade arrived. They were assessed on scene by LAS as a precaution.
The Brigade’s fire investigators believe the fire was caused by a halogen heater catching curtains alight.
A London Fire Brigade spokesperson said: “Fires involving heaters like this are all too common. They usually start when items, like clothes or bedding, are placed too close to the heater and ignite.
“It’s absolutely vital that heaters are kept well away from curtains, bedding or furniture and are never used to dry clothes.
“It's also important to always sit at least a metre away from the heater, as it could set fire to your clothes or your chair and position them where they won’t be knocked over."
The Brigade was called at 0835 and the fire was under control by 0953. Fire crews from Northolt, Wembley, Harrow and Southall fire stations were at the scene.
Firefighters’ tips for using portable heaters safely