How to fit a chimney balloon

Inspired by a helpful UK guide. This walk-through draws on "How to stop draughts down your chimney, with a chimney balloon", a practical UK video demonstrating the straightforward installation process. It is short, clear, and worth a watch before you buy your balloon — particularly for the part on choosing the right size.

1. Make sure the fireplace is genuinely unused

A chimney balloon is only for flues that are not in regular use. If you light a fire and forget the balloon is in, it will melt and potentially block the flue — which is dangerous. If there is any chance you will use the fireplace through winter, consider a removable chimney sheep (wool plug) instead, which deflates more obviously when heated.

For a gas fire that has been capped off, or a decorative fireplace that has never been used, a balloon is ideal.

2. Measure the flue opening

The balloon fits inside the flue throat, just above the fireplace opening. You need to know the width and depth of the throat — usually around 23 × 23 cm for a standard Victorian or Edwardian breast, but older or wider fireplaces can be much larger.

Chimney balloons are sold in standard sizes: 9″×9″, 12″×12″, and 18″×9″ are the most common for UK homes. When in doubt, go slightly larger — you can squeeze an oversized balloon into a narrower throat, and a bigger balloon forms a tighter seal.

3. Check for debris and birds’ nests

Stick your head in and have a look upward before you start. Loose soot, old nesting material, or rubble from the fireback can fall when you push the balloon up. Lay down some old newspaper or a dust sheet in the fireplace. Worth doing.

If there is an active birds’ nest present, leave it alone. Installing a balloon with a nest above it would cause problems when the birds return in spring.

4. Partially inflate the balloon

The balloon comes with a short plastic inflation tube. Blow into it until the balloon is about half-full — soft enough to compress easily but large enough to stay in position. You will inflate it further once it is in place.

Some people use a small foot pump. Mouth inflation is fine though — you are not blowing it up very hard at this stage.

5. Insert the balloon into the flue

Reach up into the fireplace throat and push the balloon up into the narrowing of the flue. Work it in gently, making sure the inflation tube hangs back down into the room where you can reach it. The balloon should sit snugly just above the damper plate level.

You will need to crouch or kneel to do this. Wear old clothes — even a swept chimney deposits soot on everything in reach.

6. Inflate it fully and seal the flue

With the balloon in position, blow into the tube until the balloon firms up against all four sides of the flue throat. Give it a gentle tug — if it stays put without slipping, the pressure is about right. Over-inflating strains the material; you want snug, not rock hard.

Tuck the inflation tube up out of sight. It should stay within reach for when you want to remove the balloon, but not trail down into the fireplace where it would be visible from the room.

7. Fit the reminder tag

This is the most important step. Chimney balloons come with a small cardboard tag on a cord that you hang in the fireplace opening — usually printed with something like “Do not light a fire — chimney balloon fitted”. Never skip this. It is the only thing standing between a forgotten balloon and a house full of smoke.

If the tag is lost, write your own and tie it to the grate or hang it from the mantelpiece.

8. Check for draughts

Hold a lit incense stick or a piece of tissue near the fireplace opening. If air is still moving, the balloon is not fully inflated or is not positioned correctly. Give it a top-up through the inflation tube and recheck. A well-fitted balloon stops draught completely.

Mind you, a small amount of ventilation is actually required if you have a gas appliance in the same room. Check the appliance documentation before sealing the flue entirely.

When to call a handyman

Call Richard if the flue throat is an awkward shape, the damper plate is missing or stuck, or you want the fireplace properly sealed off permanently. A chimney balloon is a temporary and reversible solution. For a more permanent fix — a draught-proof register plate or a capped pot — that is a different job and usually worth doing properly.