We need to know what type of chimney or flue you currently have. You will have one of the following: Brick Chimney, Pre-Fabricated Flue, Pre-Cast Flue, Balanced Flue, Power/Fan Flue, No Flue or Chimney.
If you’re unsure which you have see out guide here.

If you are just replacing your old inset gas fire with a new one and not replacing your fireplace it will help if you can bring in your old fire instructions and a couple of pictures of your existing fire.

If you don’t have the old instructions then some approximate sizes of your fire (width, height, depth) and fire information from the data plate of the fire (located on the fire behind the fret) will help us.

Sometimes people wish to change from an outset hearth mounted radiant brick type fire to a more modern inset living flame fire, without changing the fireplace.

This is possible but you will need the existing fire removing so we know the hole size you have to take an inset fire. (width, height, depth). A gas safe registered installer is required to remove your existing fire, this service is available at a small cost payable directly to the gas safe registered installer.