insulating chimney (fireplace being blocked up)

s7ryf3925pivug · 07-11-2019 12:53pm #1

we are removing our stove and blocking over the fireplace. I guess the chimney is basically a hole in the insulation of our house now. Any ideas about insulating it? I suppose that liquid foam stuff might be practical? There are studies saying it basically never stops off-gassing though so I probably won't do that.

I suppose a non-permanent solution might be preferable also. The stove is in the kitchen, which is only ever too hot so we absolutely never use it and it is pretty obtrusive. Would it be possible to make a fireplace on the other side, which is a sitting room? Or is this a bad idea from a structural PoV?

listermint · 07-11-2019 2:28pm

Top should be sealed with something like this

https://www.roofingoutlet.co.uk/products/197-c-cap-chimney-cowl

Bottom can be boarded up but should have a vent. This allows chimney stack to breathe insuring there isn't water originated structural problems.

If looking to seal more permanently then the cap can be sealed over with lead or similar capping and the flue can be filled with vermiculite like substance to stop any air flow. Also sealing the bottom of flue with metal grate or similar. Then board up fireplace.

Darando · 07-11-2019 4:22pm

Priced a company to supply & fit 2 of these to the existing stack and price was 120€ all in.

Haven't got around to checking elsewhere for a better price so if anybody else knows of a place (Dublin)

listermint wrote: »

Top should be sealed with something like this

https://www.roofingoutlet.co.uk/products/197-c-cap-chimney-cowl

Bottom can be boarded up but should have a vent. This allows chimney stack to breathe insuring there isn't water originated structural problems.

If looking to seal more permanently then the cap can be sealed over with lead or similar capping and the flue can be filled with vermiculite like substance to stop any air flow. Also sealing the bottom of flue with metal grate or similar. Then board up fireplace.

s7ryf3925pivug · 07-11-2019 4:54pm

Builder is doing it and it's permanent. Is there a need for a vent at bottom if it's made airtight at the top?
Builder thinks insulation will make little difference once it's sealed up. That doesn't make sense to me really as it seems like just having a big gap in your insulation.

Calahonda52 · 08-11-2019 4:39pm

listermint wrote: »

Top should be sealed with something like this

https://www.roofingoutlet.co.uk/products/197-c-cap-chimney-cowl

Bottom can be boarded up but should have a vent. This allows chimney stack to breathe insuring there isn't water originated structural problems.

If looking to seal more permanently then the cap can be sealed over with lead or similar capping and the flue can be filled with vermiculite like substance to stop any air flow. Also sealing the bottom of flue with metal grate or similar. Then board up fireplace.

.
If the vermiculite ever gets wet it expands so could cause issues.
recycled glass is the way to go

whizbang · 09-11-2019 12:07am

Chimneys are notorious places for water ingress. Basically, you need to remove it altogether to prevent any chance of water getting in.
Then and only then can you make it airtight.

s7ryf3925pivug · 09-11-2019 3:06am

The consensus seems to be that ventilation is important to avoid damp issues. I guess I'll need to make sure hes having ventilation at the top. I can just drill holes myself for ventilation at bottom if that's simpler.

Does the fact it is a stove affect this?

One approach I found online was to add a vent in the attic instead of at ground level, and fill it with polystyrene beads up to the level of the attic insulation. This would address my original query about insulation. Does it sound like a good idea?

listermint · 09-11-2019 8:55am

Gerardo Some Spirits wrote: »

The consensus seems to be that ventilation is important to avoid damp issues. I guess I'll need to make sure hes having ventilation at the top. I can just drill holes myself for ventilation at bottom if that's simpler.

Does the fact it is a stove affect this?

One approach I found online was to add a vent in the attic instead of at ground level, and fill it with polystyrene beads up to the level of the attic insulation. This would address my original query about insulation. Does it sound like a good idea?

That should be sufficient

william · 11-12-2019 11:03pm

Gerardo Some Spirits wrote: »

One approach I found online was to add a vent in the attic instead of at ground level, and fill it with polystyrene beads up to the level of the attic insulation. This would address my original query about insulation. Does it sound like a good idea?

I read before that this is fine for internal chimneys but not ones on external walls. Don’t remember the technical aspects.

listermint · 11-12-2019 11:12pm

william wrote: »

I read before that this is fine for internal chimneys but not ones on external walls. Don’t remember the technical aspects.

I don't believe that has any impact. The only concern is water ingress. Polystyrene won't absorb it and the vent I marked above offers escape for any moisture.

Why would internal or side enveloped Chimney matter? Suggest finding the technical aspects...

GreeBo · 12-12-2019 9:45am

Is off-gassing not a concern when blocking up a chimney?

listermint · 12-12-2019 11:13am

GreeBo wrote: »

Is off-gassing not a concern when blocking up a chimney?

Off gasing what? have you no ventilation in your house?

If you are relying on a chimney to off gas your home then id suggest moving out. Theres bigger problems at play...

GreeBo · 12-12-2019 1:30pm

listermint wrote: »

Off gasing what? have you no ventilation in your house?

If you are relying on a chimney to off gas your home then id suggest moving out. Theres bigger problems at play...

Years of crap, soot, etc going up the chimney and not all of it going out (otherwise we wouldnt need to clean chimneys ever)
If you block the top off, where is any of that going?

listermint · 12-12-2019 1:42pm

GreeBo wrote: »

Years of crap, soot, etc going up the chimney and not all of it going out (otherwise we wouldnt need to clean chimneys ever)
If you block the top off, where is any of that going?

Stays put...

Clean it before you fill it.

Any details on what 'off gassing' chimney soot has ?

GreeBo · 12-12-2019 2:12pm

listermint wrote: »

Stays put...

Clean it before you fill it.

Any details on what 'off gassing' chimney soot has ?

I'd say it very much depends on what was burnt over the life of the fireplace.

I dont believe cleaning a chimney is to prevent off gassing, more so to stop chimney fires.

FlipperThePriest · 12-12-2019 2:38pm

The soot left in a chimney is nothing more than solid carbon particles. Nothing gaseous about it. Any gas was released up the chimney during burning. When you block up a chimney, whatever remains isn't going anywhere.

GreeBo · 12-12-2019 6:05pm

zippy84 wrote: »

The soot left in a chimney is nothing more than solid carbon particles. Nothing gaseous about it. Any gas was released up the chimney during burning. When you block up a chimney, whatever remains isn't going anywhere.

I think that's an oversimplification tbf.
Soot is the result of incomplete combustion (otherwise there wouldnt be anything left) and hence results in formation of dioxins and other toxins depending on what has been burnt.

That crap is sitting in your chimney clinging to the inner surfaces.
An open (working) chimney extracts any loose soot or off gassing out into the atmosphere, if you block the to of the chimney you remove the draw and also the exit path for this stuff.
Add in a vent brick etc at the bottom and you are only giving it one place to go and thats into your house.

I'm not categorically saying that this is an issue, I'm suggesting that its something I would investigate before just blocking it up.

listermint · 12-12-2019 8:51pm

You've no evidence of this though tbf.

You've provided no information on it or off gassing from it or anything to do with blocking the chimney.

So you can understand why I've asked for details several times.

Often opinion is mistaken for facts here.

Mr Magnolia · 12-12-2019 10:33pm

Ah here, off-gassing from soot residue in a domestic chimney stack?!

I'd have no hesitation in blocking it up in the living room and insulating. Stick a cowl on the topside to stop water ingress similar to the one linked below.

https://www.vent-axia.com/range/unitex-roof-cowl-system

GreeBo · 13-12-2019 1:57pm

listermint wrote: »

You've no evidence of this though tbf.

You've provided no information on it or off gassing from it or anything to do with blocking the chimney.

So you can understand why I've asked for details several times.

Often opinion is mistaken for facts here.

Equally I only asked was it a concern in my first post.
"Is off-gassing not a concern when blocking up a chimney?"

I've seen no evidence its an issue or indeed a non-issue, hence why I said
"its something I would investigate before just blocking it up."

Dismissing it as "just soot" without any evidence to support the claim that its harmless, considering you are going to be living with it for decades wouldn't make me comfortable, I'd get it confirmed that its a non issue and then block/insulate/etc away with confidence.

listermint · 13-12-2019 2:00pm

GreeBo wrote: »

Equally I only asked was it a concern in my first post.
"Is off-gassing not a concern when blocking up a chimney?"

I've seen no evidence its an issue or indeed a non-issue, hence why I said
"its something I would investigate before just blocking it up."

Dismissing it as "just soot" without any evidence to support the claim that its harmless, considering you are going to be living with it for decades wouldn't make me comfortable, I'd get it confirmed that its a non issue and then block/insulate/etc away with confidence.

You will have to back up your claims with some actual detail though. It appears you are just asking scaremongery style questions for no apparent reason.

GreeBo · 13-12-2019 2:15pm

listermint wrote: »

You will have to back up your claims with some actual detail though. It appears you are just asking scaremongery style questions for no apparent reason.

What claim though?
Soot isn't some inert thing, I dont think its unreasonable to ask the question if its safe to block it up and ignore it.
If you or the OP are happy to ignore it, then fine, all I did was ask the question, I haven't seen anything that would prove to me that it's safe to ignore it other than "ah sure it's just soot".

listermint · 13-12-2019 2:40pm

GreeBo wrote: »

What claim though?
Soot isn't some inert thing, I dont think its unreasonable to ask the question if its safe to block it up and ignore it.
If you or the OP are happy to ignore it, then fine, all I did was ask the question, I haven't seen anything that would prove to me that it's safe to ignore it other than "ah sure it's just soot".

You are scaremongering facebook style.

Soot is a danger if you inhale it or ingest it (a good bit of it or overtime) you are making up claims about off gassing. Yes it was a claim and you made it.

Then you revert to 'Well if you are ok with it then...' which is a terrible argument, You have provided no evidence of your claims

GreeBo · 13-12-2019 2:57pm

listermint wrote: »

You are scaremongering facebook style.

Soot is a danger if you inhale it or ingest it (a good bit of it or overtime) you are making up claims about off gassing. Yes it was a claim and you made it.

Then you revert to 'Well if you are ok with it then...' which is a terrible argument, You have provided no evidence of your claims

1) If you can point me to where I made any claims then I'll gladly correct those posts.
2) I didn't give any argument, I pointed out that I wouldnt be happy to do anything without getting the facts, either way.
3) No one has provided any evidence that it is safe

It makes zero difference to me what the OP (or indeed anyone else) does in their home, my point is that I personally would get confirmation that it wasn't an issue before doing anything with my chimney.

/out.

Mr Magnolia · 13-12-2019 3:39pm

No one has presented evidence that blocking up the chimney won't lead to hiv either. Doesn't mean it's a possibility.

listermint · 13-12-2019 5:08pm

GreeBo wrote: »

1) If you can point me to where I made any claims then I'll gladly correct those posts.
2) I didn't give any argument, I pointed out that I wouldnt be happy to do anything without getting the facts, either way.
3) No one has provided any evidence that it is safe

It makes zero difference to me what the OP (or indeed anyone else) does in their home, my point is that I personally would get confirmation that it wasn't an issue before doing anything with my chimney.

/out.

From who ? Be specific

14-12-2019 4:42am

(Note: I dont know all the correct chimney terminology here, so bare with me!)

We have a chimney that runs up through the centre of our house (ie; we have access to both sides, of which each is a fireplace, in two different rooms, but our breast doesn't touch against next door's house).

We got central heating installed about.. 15 years ago, I'd guess? My dad was the DIY expert at the time, and the approach taken was to stick some plywood over the 'hole' of the fire, and ignore the actual chimney on the roof.

About 3 years ago, I was renovating the downstairs kitchen and i took away the ply covering, and inside was fine. Dry, clean and nothing noteworthy was going on.

About a year ago I did the same in the sitting room. Our sitting room has, for as long as I remember, had silverfish issues at night (they never bothered me, but they were always present). The reason for this became clear, when I removed the ply, as the fireplace wasn't cleaned out properly before it was sealed, or failing that, if it was, soot that was inside the stack had fallen over time, and I was left with a fair few black bags of soot to remove from the fireplace (I'm guessing he just never bothered cleaning it out before sealing it off).

Nowadays, I have cleaned both out, covered them with plywood, but also covered the chimney on the roof with lead flashing. It's been seen by a few tradesmen wandering in and out (including a builder who sealed it in the house, and a roofer who did the lead flashing) and nobody ever said anything about allowing it ventilation.

But nonetheless, in the 15 years or so it's been sealed (just downstairs/internally), we've had no issues with dampness, mould, etc. except the few silverfish on one side that wasn't cleaned out, but that's really a self-inflicted issue, I suppose. I'd almost miss the little buggers

Also in the last 3 years (since the lead flashing went on top) we've had no issues either (that I'm aware of).

LenWoods · 14-12-2019 11:56am

I've blocked our chimney few years ago using a C-cap purchased from an online shop based in the isle of man which is linked in my thread here; I've also put in a chimney balloon and vent in the side of the chimney base,

No heat loss and no need to insulate any further since the air flow is reduced.
Link: https://www.fordownersclub.com/forums/topic/80864-living-room-project/

insulating chimney (fireplace being blocked up)

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