Buying Guide
Best Chimney Draught Excluders UK 2026
Updated August 2026
An unused chimney is a direct hole to the sky. Cold air pours down it 24/7, making your room feel cold even with the heating on. A chimney draught excluder blocks this draught completely — and costs £15-30. If you have a fireplace you don't use regularly, this is one of the highest-impact draught fixes in your home.
Quick answer
Our top pick: Chimney Sheep (natural wool flue blocker)
£20–£30 on Amazon
Best overall: Chimney Sheep (natural wool, reusable, fits any chimney, £20-30). Budget option: chimney balloon (inflatable, £10-15). Remember: ALWAYS remove before lighting a fire.
Check Price on Amazon →How much heat does an open chimney lose?
An open flue behaves like a permanently open window roughly the size of a laptop. Warm air rises up the stack and cold air is pulled in through every gap in the room to replace it — the stack effect. Industry estimates put the loss at 40-60 cubic metres of heated air per hour from a typical unblocked domestic chimney.
In heating-bill terms, blocking one unused chimney typically saves in the region of £50-£90 a year for a UK household on current tariffs. An excluder costing £20 pays for itself in a single winter, and often within a couple of months.
The comfort difference is more noticeable than the money. The draught from a chimney flows down the breast and across the floor, which is exactly why the room feels cold at ankle level even when the radiators are hot.
Chimney sheep vs chimney balloon
| Factor | Chimney sheep (wool) | Chimney balloon (inflatable) |
|---|---|---|
| Price | £20–£30 | £10–£15 |
| Fitting | Push up on a handle — 30 seconds | Inflate in place — a few minutes |
| Lifespan | Many years — wool is durable | 1–3 years before it perishes or punctures |
| Moisture handling | Breathable — wool absorbs and releases damp | Sealed — can trap moisture in the flue |
| Removal | Pull the handle down | Deflate and pull out — messier with soot |
| Best for | Fireplaces you may light occasionally | Cheap fix for a fireplace never used |
Both work. The wool option wins on lifespan and on breathability, which matters because a completely sealed flue can leave damp patches on the chimney breast.
Products that pair with a chimney excluder
BLACK+DECKER Thermal Leak Detector
Point it at the fireplace opening and the readout drops sharply if the flue is losing heat. Most people find their chimney is only one of several leaks — the detector stops you fixing the wrong thing and lets you tackle the rest in the right order.
Pros
- Shows exactly where cold air enters the room
- Confirms the chimney is the culprit before you buy
- Finds door, window and floorboard draughts too
- Reusable across the whole house
Cons
- Costs more than the excluder itself
- Needs a temperature difference to work
Who it's for: Working out whether the cold room is the chimney, the windows, or both
Check Price on Amazon UK →Radflek Radiator Reflector Panels
A chimney breast is a large mass of cold masonry that soaks up heat from any radiator near it. Reflector panels bounce that heat back into the room instead. Fitted alongside a chimney excluder, the room warms up noticeably faster.
Pros
- Reflects radiator heat back into the room
- Ideal on the chimney breast wall, which is always cold
- Fits in minutes with no tools
- Lasts for the life of the radiator
Cons
- Only helps radiators on external or chimney-breast walls
Who it's for: Radiators mounted on a cold chimney breast or external wall
Check Price on Amazon UK →How to fit a chimney draught excluder
- Measure the flue, not the fireplace opening. Reach up inside and measure the throat — the narrow point just above the opening. Most UK flues are between 25cm and 45cm across.
- Sweep first if it has been years. Loose soot and old nest debris will fall on you and the excluder. If the chimney has not been swept in five years, get it swept before blocking it.
- Wear goggles and old clothes, and lay a dust sheet. Everything you dislodge lands in the hearth.
- Push it up into the throat until it grips. A wool excluder should compress slightly against the sides. A balloon goes in deflated and is then inflated until firm.
- Leave the handle or tag visible. This is both how you remove it and the reminder that the flue is blocked.
- Hang a warning tag in the hearth. "CHIMNEY BLOCKED — REMOVE BEFORE LIGHTING FIRE". Non-negotiable if anyone else uses the room.
When to remove it — before lighting any fire
Always remove the excluder before lighting a fire. A blocked flue pushes smoke and carbon monoxide straight back into the room. This is the single serious risk with chimney draught excluders and it is entirely avoidable.
Never fit one in a flue serving a working stove, gas fire, or any gas appliance — including a back boiler. Those flues must stay clear at all times.
Fit a carbon monoxide alarm in any room with a fireplace, blocked or not. They cost under £20 and are a legal requirement in rented homes with a solid fuel appliance.
Take the excluder out for a week each spring to let the flue air and dry out, then refit it in autumn.
Alternative: a register plate
The permanent option for a fireplace you'll never use
A register plate is a sheet of steel fitted across the flue at throat level and sealed to the brickwork. It blocks the chimney permanently and completely, and it is the right answer if the fireplace is decorative and will never be lit again.
It must include a small permanent vent — typically an airbrick or a capped vent fitting — so the flue can breathe. Without one, moisture is trapped in the stack and you get damp staining on the chimney breast within a year or two. Fitting one is a job for a competent DIYer or a chimney specialist, and costs £100-£250 installed.
For everyone else, a removable excluder gets you 90% of the benefit for £20 and keeps your options open. See our whole-house draught-proofing guide for the rest of the room.
Warning
Never block a live flue
If the fireplace serves a working stove, open fire, gas fire or back boiler, do not fit any kind of excluder. Blocked live flues cause carbon monoxide poisoning. If you are unsure whether a flue is in use, have it checked before blocking it.