Why does cold air come down the chimney when it is not lit? Causes and solution
The chimney flue remains connected to the outside even when there is no fire, so cold air can come down it just as smoke goes up it when the fire is lit. A flue damper or adjustable vent is the most common solution.
The chimney flue remains connected to the outside even when there is no fire, so cold air can come down it just as smoke goes up it when the fire is lit. A flue damper or adjustable vent is the most common solution.
It is one of the most common complaints we hear in winter, especially with open fireplaces that are only used on some weekends: “I can feel a cold draught coming from the chimney even though it is not lit.” It is not your imagination—it is the physics of the flue itself, and it can be fixed without building work.
Why it happens: the flue does not “close” by itself
A traditional open fireplace is essentially a tube connecting your living room directly to the outside. When the fire is lit, hot air rises and exits through the chimney draught. When it is off, that same tube is still there, and if the outside air is colder (and therefore denser) than the air in the room, it can flow down the flue, creating the draught you feel near the fireplace opening.
Solutions, from the simplest to the most complete
- Chimney damper: a metal flap inside the flue, just above the fireplace, that is manually closed when the chimney is not in use. It is the most common solution in traditional fireplaces, and many already have one fitted as standard, although over time it can become stuck or misaligned.
- Inflatable chimney draught stopper or pillow: a device placed inside the flue when you will not be using the chimney for a long period (for example, from May to October), and removed before lighting it again. It is widely used in chimneys without a working damper.
- Thermal curtain or glass screen across the fireplace opening, which blocks the direct draught into the room without sealing the flue itself.
The mistake to avoid
If your home has a gas appliance or another combustion system that in any way shares ventilation with the fireplace area, never permanently or hermetically seal the flue without professional assessment. Even when unused, the chimney may still play a ventilation role in the home's overall installation. A damper that can be opened and closed is always safer than a homemade fixed plug.
When to call a professional
If you feel much more draught than seems normal, if the damper does not close properly or you cannot identify it, or if the cold sensation is accompanied by damp or dripping inside the fireplace, an inspection is advisable. There may be a problem with the chimney cap or the condition of the inner lining, rather than simply an airflow issue.
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We check whether it works properly or whether you need an additional chimney draught stopper.
Frequently asked questions
Do all chimneys have a damper?
No. Many older masonry fireplaces do not have one. In these cases, a chimney draught stopper or a screen are the most common alternatives.
Can I block the flue myself with something improvised?
It is not advisable. An improvised plug may fit poorly, fall into the flue, or cause damp if it allows no ventilation at all. It is better to use a device designed for the purpose.
Does a cold draught mean there is a problem with the flue?
Not necessarily. It is normal in open fireplaces without a closed damper. But if it is very strong or accompanied by damp, it is worth having it checked.
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