How do I bathroom / kitchen / extension? etc.

Usual disclaimer and it may not matter but they are not great for your health, or those of your neighbours.

They’ll uncap the chimney and drop a liner down it. You’ll need a new pot too so a bit of remedial work required if it’s a mess up there. Depending on what’s going on in your fireplace there might be some work required there too. Then it’s a case of hooking the burner up to the liner.

Obvs. the bigger the mess up there and the more difficult the access the more pricey it is.

We had one fitted a few years ago, we originally had an open fire but wanted to convert to a burner for efficiency. We had an endless supply of wood from my brother's tree surgery business.

I think the total cost was around 3K for the (Burley) burner, flue liner, cowling, widening the opening, granite hearth and making good (plastering etc).

Always use seasoned wood (do not buy kiln dried, season it yourself for at least 12 months) and always burn hot (do not slumber).

We paid around £4k a few years ago:

Wiking Stove
Slate hearth
Metal plate to close internal chimney aperture (was previously an open fire)
Flue
Some flue packing Vermiculite stuff (quite a few bags)
New chimney pot and a tiny bit of rendering work
Removal of some very old dead birds

We don’t use it daily but being up in Scotland and having access to fallen wood we dry as much as we can and use it when it’s super cold.