In our last post, we covered the key reasons why it’s wise to block an unused chimney, from cutting heat loss to keeping out unwanted guests. But how exactly do you go about doing it safely and effectively? There are a few options, depending on your budget, the condition of the chimney, and whether you'd like the option to reopen it in the future.
Here’s a guide to the most common methods used to block an unused chimney – including some important dos and don’ts.
Chimney Balloon (Chimney Pillow) or Chimney Draught Excluder
Best for: Temporary or semi-permanent draught-proofing
Cost: Low (£15–£30)
Chimney balloons or pillows are one of the easiest and cheapest ways to block a chimney. Made of durable plastic or rubber, they’re inserted into the flue and inflated to create a seal that stops draughts and debris from entering. Many UK homeowners choose this option because it's simple to install yourself and easy to remove if needed.
An alternative to this is a draught excluder or sheep, which works in a similar way but is made from breathable, natural materials such as wool, thereby allowing some ventilation.
DO leave a small tag or string hanging down into the fireplace so you can retrieve it easily later. DON’T install too close to the chimney opening – allow some airflow to avoid condensation and damp build-up.
Chimney Cap (Top Cap or Cowl)
Best for: Preventing rain and animals entering from above
Cost: Moderate (£30–£100 + fitting)
A chimney cap (also called a cowl or rain guard) is fitted at the top of the chimney pot to stop rain, birds, and debris from getting in, while still allowing some airflow. This is especially important in the UK, where rain and nesting birds are common.
It’s recommended that you get a professional roofer or chimney specialist to fit one safely, especially if access is tricky.
Permanent Blocking
Best for: Long-term disuse or chimney removal
Cost: Higher (typically £200–£600)
For a more permanent solution, you can have the flue sealed off by a professional. This might include bricking up the fireplace opening and installing an air brick or vent to allow airflow. The top of the chimney may also be capped and pointed to prevent weather damage.
This is the most durable option and can significantly reduce maintenance, but it requires professional installation to avoid moisture issues or structural problems.
DON’T block without ventilation: a common mistake is sealing off a chimney entirely without leaving any airflow. Chimneys, even when unused, help your home "breathe". Without some ventilation, you risk damp patches and stale air. Always allow a small vent or choose a breathable draught excluder to keep things balanced.
There are a range of options to suit different budgets and needs; if in doubt, consult a local chimney sweep or roofer – they’ll be able to assess the condition of your chimney and recommend the safest and most effective way to block it. For more guidance, follow us on Facebook or X.