Blocking up a fireplace

rob316

I bought a house recently and I want to block up one of the fireplaces. The chimney has been swept, I've removed the fireplace black to the block.

I'm getting conflicting information online on what I should do. I was going to cap the chimney, put a vent on the side of the chimney in the living room, board up the fireplace and plaster it. Is this enough or does it require insulation at the bottom too?

Appreciate any advice

Thanks

Rob

listermint

https://www.boards.ie/discussion/2058316584/blocking-up-a-fireplace

There's a condensation risk with chimney stacks which has the ability to cause problems. Traditional advice is to allow some air to ventilate the stack.

What I did because I didn't want to ventilate it as that for me creates an airleak and draught.

I plugged the bottom of the flue with a piece of EPS shaped like the flue (circular) which acted as a bung. I filled the stack with loose EPS fill to about 500 mm belo2 the top of flue. Fire rated stuff. And then I capped the top of flue with a chimney 'D cap' which allows some airflow out the stack.

I did this to 2 chimney stacks in our house about 4 years ago. Zero problems no draughts.

rob316

https://www.boards.ie/discussion/comment/121189243#Comment_121189243

I like that idea, better than chasing out a wall vent and as you said airtight. How much EPS fill did ya need to fill the stack? Mines a 2 storey

listermint

https://www.boards.ie/discussion/comment/121189395#Comment_121189395

Hmmm can't recall. I estimate it was probably 3 black bags full for the 2 stacks. Bungalow height so roughly 2x 6 Meter stacks.

I bought faaaar to much of it and had a huge sack left over which hung around in the garage for 2 years until gave it away to someone for insulation wall fill for his shed.

rob316

https://www.boards.ie/discussion/comment/121189463#Comment_121189463

I was also thinking instead to put a vent in the chimney stack in the attic?

listermint

https://www.boards.ie/discussion/comment/121189675#Comment_121189675

No harm it would at least add movement through the top of the stack.

I didn't however no problems so far. Have been up checking both stacks recently.

jack of all

I did a spec for just such a job last year. Fireplace opening was blocked up and the flue was filled with a special glass bead insulation (name escapes me), that's inert and won't absorb moisture. Flue to be filled to say 300mm above the level of the loft insulation, with a permanent air vent fitted in the stack, another 150mm above this again, venting into the loft space. Finally the chimney is fitted with a cowl, to allow air flow but prevent rain and bird entry. Keeps the stack condensation free, reduces heat loss and provides additional roof ventilation.

dathi

https://www.boards.ie/discussion/comment/121198844#Comment_121198844

geocell foam glass gravel ?

listermint

https://www.boards.ie/discussion/comment/121208519#Comment_121208519

Any innert material that doesn't absorb moisture will really do tbh.

rob316

https://www.boards.ie/discussion/comment/121189243#Comment_121189243

Would you have a link to an example of the materials you used, can't seem to find the right product. Thanks

listermint

Pm

jack of all

Geocell foam glass to fill the flue ...

william

https://www.boards.ie/discussion/comment/121198844#Comment_121198844

Hi.

Re: "with a permanent air vent fitted in the stack, another 150mm above this again, venting into the loft space."

I understand the 2nd vent in the attic space. However, is the first 'permanent' one in the attic as well? What sort of diam would be recommended?

I was thinking of adding the glass gravel (e.g. https://geocell.ie/) and running a narrow diam (say 20mm) perforated pipe top to bottom for ventilation. Would have to puncture a standard pipe or conduit to create the air holes - most perforated only comes 110mm +.

Many thanks,

William

listermint

https://www.boards.ie/discussion/comment/121285312#Comment_121285312

Tbh that's defeating the purpose. Your creating uncontrolled airflow just smaller diameter from your living room. Pointless, you may aswell leave it as is

jack of all

+1 on the above, I meant 1 vent only, placed at 150mm above level of the filling in the flue.

william

Thanks for the advice. Seems very possible to do.

We have chimney caps in place (with metal attachments) and they have been a nightmare. They eventually corrode and the metal releases from the cap causing it to flap and resonate down the chimney. Are the clay ones that insert into the pot good enough? something like this https://www.goodwins.ie/products/Chimney-Flue-Vent-Clay-180mm.html

tomekJ

Hi All,

I am planning to block fireplace that was not used for years to eliminate draft and heat loss. It's a bungalow from 90s. I know if this is not done properly it will lead to issues. I was advised that C cap cowl on top of chimney is needed to prevent birds and rain getting in. Then on the bottom I was planning to use some kind of insulation that does not absorb moisture (don't know yet what to use) also is it ok to just use enough to block the "throat" ?then I was planning to block with plywood and plasterboard fully. So that would mean that the bottom is fully cealed off but air should still get in from the top. There are no air vents, at least I didn't see any. Do I need to drill them in the attic??

Calahonda52

Why post it three times in 3 different places?