Making fireplaces airtight

[jayc89]

It's a while off, but as I work by way around the house insulating and improving airtightness, I'm going to eventually reach a couple of open fireplaces. One has a stove fitted, so is lined and has a register plate between the brickwork and the slate tiles. The other is currently back to brick with a bung shoved up it. 

 

The one with the stove in will be a PITA to do anything with, it's unlikely we'll get the tiles back off without damaging them and even if we could, even 25mm insulation would likely mean the space around the stove no longer complies with regs, so I'm mainly looking to focus on airtightness around the register plate junction. What's the best option with this one? Remove the plate, glob it up with some sort of heat retardant sealant, refit and drop Vermiculite or similar from above around the lining?

 

For the one that's back to brick, the plan is to build this out and have a media wall installed there, so we have more flexibility. I'm thinking of framing it out, to support the new inset fire and TV and using spray foam insulation to fill the gaps behind, cutting it flush around the frame once set - which should tackle insulation and airtightness at the same time?

 

 

[George]

Register plate and flue should already be relatively airtight - it is all intended to keep leaking flue gases out of the home. You could even get HETAS to do a smoke test.

 

But a heat resistant silicone sealant could be used for any tiny gaps if there are any.

 

 

The disused open chimney will need ventilation to prevent damp. Usual approach is a closable vent into the room and a ventilated cowl at the top. However, you can seal it to the room if you can put a vent on the outside of the wall into the flue. That's what I did with my upstairs disused flues. 

 

Spray foam I wouldn't use - just frame it out and tight fit insulation board.

 

Edited January 12, 2023 by George