Cold Plug – Winter Safety Advice

A ‘cold plug’ in your flue can be an unexpected issue during the colder weather. It is an invisible plug of cold air that can form in your chimney when temperatures drop significantly, and the chimney is left to go cold. This can result in the flue being plugged, which pushes smoke back down and out of your stove.

It can occur overnight during a sudden drop in temperature when your stove is not on or when a clear chimney has not been used for a long time. Also, it’s more common to happen in a twin wall flue system as they can be more exposed.

There are measures you can take to limit the risk of a cold plug:

  • Leave your stove door open at least 30 minutes before lighting and when not in use.
  • Using the top down method of lighting a fire.
  • Starting with a firelighter can be effective way to warm the flue.

Ideally, you want to gently increase the internal temperature of your chimney to remove the cold air plug.

Your local HETAS Registered Installer or Sweep & Service Technician will be able to offer further seasonal tips when they complete your installation, annual service, or regular sweep.


HETAS, Severn House, Unit 5 Newtown Trading Estate, Green Lane, Tewkesbury, GL20 8HD