How to Measure Your Chimney Flue

The sheep works by being a little bit bigger than the flue so it can grip onto the sides and hold itself in place. The amount of overlap doesn’t matter too much as the felt is squashy and can fit into a range of gaps. If you have a round flue, you want a round sheep that is an inch or so larger. 

If you have a square, oblong, D-shaped, trapezium shaped or similar use the sizing chart below to help you. Remember that a round sheep will squash into a round or oblong hole.

If you have a chimney flue that doesn’t match any of the sizes given you may need to have one made specially – let us know your chimney dimensions and we can give you a quote for getting a bespoke one made.

Right. If you have a head torch it helps for this bit, but if not just get a regular torch or light and prop it up so you can see up your chimney. Mind out for soot getting in your eyes. Get a tape measure. If you have a round flue, measure the diameter.

If you have any other shaped flue, measure the depth and width of the narrow part just above the fireplace. Don’t worry if it’s an odd shape, just measure the longest parts and the wool felt will squash in to fit. While you’re in there, check the height of the part where the sheep will fit above the fireplace.

Each sheep comes with a handle and extension rod with a total length of 12” / 30cm / 300mm. It’s important to be able to see the end of the handle at the top of the fireplace as a reminder to take it out before lighting a fire – order extra rods if you need to. If the narrow bit is much higher up, it’s easier to put a larger sheep in lower down.

(Find out more about building regulations regarding chimneys and flues)