If you are fitting a stove to a class 1 chimney and are not using a flue liner as you are relying on the chimney breast to draw the fumes away its important you use a register plate.
These are designed to seal the chimney breast to the flue pipe increasing the draw through the stove so it can be controlled correctly.
We sell 6 different sizes of register plates and keep them in stock too for quick despatch so you can choose which size is closest to the sizes of the chimney breast they of course can be cut to size so alwyas choose larger than smaller.
They come complete with fixing brackets which are then held in place using a self tapping screw, to ensure a perfect fit Castfireplaces would suggest sealing round the sides of the register plate and again round where the flue goes through the collar forming a nice seal, again this helps with controlling the stove but then also no debris will fall onto the top of your new stove.
Finally make sure you do not seal the inspection flap this will be needed for access and cleaning the chimney when being swept and this little flap is simply removed so the chimney sweep can hoover the top of the plate removing soot once the chimney has been swept.
So a little more advice from us here to help our customers.