Block chimney draughts with a chimney balloon

Fit a chimney balloon to block draughts from an unused chimney, checking safety first.

CB-01Confirm the flue is not in useCheck no gas fire, gas boiler flue, or solid fuel stove vents into this chimney. Never fit a balloon if an appliance uses the flue, as trapped fumes can cause carbon monoxide poisoning. If you are not sure, ask a Gas Safe registered engineer or a HETAS installer before going any further.

CB-02Clear the room and protect the hearthMove furniture and rugs away from the fireplace. Lay a dust sheet over the hearth, because soot and old debris often fall when you disturb the flue.

1 each · Dust sheet

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CB-03Check for birds, nests or batsShine a torch up the flue and look for nests, twigs, feathers or droppings before fitting anything. Bats are a protected species in the UK, so if you see any sign of a roost, stop straight away and do not disturb it. Contact the Bat Conservation Trust for advice before proceeding.

RULES

1 each · Torch

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KNOW THE RULES

The Wildlife and Countryside Act 1981 makes it an offence to disturb a bat roost. If you find any evidence of bats, get advice before continuing.

CB-04Measure the flue openingMeasure the width of the flue where the balloon will sit, usually just above the fireplace opening or at the register plate. Take the smallest measurement you find, since the balloon needs a snug fit to stop draughts properly.

1 each · Tape measure

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CB-05Buy the right size chimney balloonChimney balloons usually come in sizes from 200-250mm, 250-300mm, 300-350mm and 350-400mm to match different flue widths. Pick the size that matches your measurement, and if you're between sizes, choose the smaller one and inflate it fully for a tight seal.

1 each · Chimney balloon (size to fit flue)

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CB-06Position the balloon in the flueWith the balloon deflated, push it up into the flue past any register plate or damper. Keep the string, tag and pump tube hanging down where you can still reach them from the fireplace opening.

CB-07Inflate to a snug fitInflate slowly using the hand pump, checking regularly that the balloon is filling the gap without straining against the flue walls. Stop as soon as it feels firm and snug. Overinflating can burst the balloon or wedge it in so tight it's hard to remove later.

CB-08Attach a visible reminder tagTie a bright tag or label to the string and drape it somewhere obvious, such as over the mantelpiece. This reminds everyone in the house that the chimney is blocked, so nobody lights a fire or connects an appliance to it while the balloon is fitted.

CB-09Check for remaining draughtsClose nearby doors and windows, then hold your hand near the fireplace opening to feel for cold air. If a draught is still getting through, check the balloon is centred in the flue and fully inflated. A fireplace draught excluder plate can help seal any remaining gaps.

CB-10Tidy up and store the pumpRemove the dust sheet and vacuum up any soot or debris that fell during fitting. Wipe down the hearth and keep the pump and any spare balloon packaging safe, in case you need to top up the inflation or replace the balloon later.

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