Hi,
I've removed a very old oil heater from its place the wall. Now I need to do something about the hole it left behind. The heater shell is quite rusted, so I may need to remove that, but it's attached to a flue outside which leads to the roof. So, if I remove the shell then I'd probably need to remove the whole flue, which becomes a bigger job.
I'd be ok with cutting off some of the protruding metal from the heater shell if it was easy to do, then put some insulation in the space and cover with plasterboard. Would this work?
What other options are there apart from bricking it up, which would be expensive?
See photos of the removed heater and outside flue below.
Thanks!

