Is it ever possible to properly insulate a disused (external) chimney?

[Andy.T]

Hi all,

About 7 years ago we filled/plastered a disused fireplace in our lounge to return it to just a flat plaster wall.

The chimney is external and an air brick was fitted to allow air to circulate along the external chimney (see photo).

The chimney is also capped with a paving slab (or similar) at the top and covered in wire mesh to prevent birds falling in (used to happen regularly!).

It's been good as gold, we've had no problems with sweating or damp patches on the lounge wall at all.

However, I'm pretty sure the lack of any insulation in the chimney means we lose a fair amount of heat through this part of the wall in the lounge and bedroom above, in winter. The air moving so freely through it presumably just sucks warmth off the interior walls.

I've measured this indoors with a thermometer in winter, and the parts of the wall with the external chimney on are a fair few degrees colder than the rest of the wall (which has cavity insulation).

My question is, is it ever possible to insulate a disused external chimney like this?

I know you "have to allow ventilation so that the air in it doesn't condense/cause sweating". But is this not because it's such a large empty void containing lots of air?

i.e. If it were filled with something like wall insulation (polystyrene beads or whatever), would that remove the need to keep it so well ventilated?

I'm just thinking about rising gas prices and trying to find places heat will be escaping that I can potentially do something about, before next winter?

I've seen the inflatable bags etc. that you can shove up a temporarily unused chimney but I wondered if there's some more permanent/better performing options to prevent heat loss from it (without causing damp in the lounge and bedroom)?

I know the other option would be to look at entirely removing the external chimney but I don't think my budget will stretch to that sadly!

Thanks,

Andy

 

[tell80]

If you have fireplace openings on two floors & both are blocked off you would be venting one flue only with the one air brick we can see?
However, if there's only the one blocked off flue for one ground floor fireplace in the chimney breast then your outside air brick will be venting it.
Were either of the flues swept before you blocked them off - I ask because the top 2m of the external chimney breast is looking like soot might be attempting to penetrate. It could, of course, be heavy weathering stains?

How would you shove an air bag up the blocked off lounge fireplace?
Pics of the lounge & the bedroom fireplace would help?

 

[Andy.T]

Hi Tell,

Thanks for replying. There's nothing to see in the lounge or bedroom internally now. It's just flat plastered/decorated walls.

The only fireplace was downstairs and that's been all bricked up for about 7 years (so yep, I'd presume just one flue).

I think the darkening at the top of the chimney is just weathering, as you say. I'm not sure how much "real" use the chimney ever saw. We moved in 17 years ago and the previous owner just had an electric fire kinda shoved in there.

The air bag wouldn't be a solution for us now that it's all blocked off internally. I was just saying that I know people use those when they just want to temporarily insulate a disused chimney.

What do you think would be the best way to miminise heat loss through the chimney whilst not inviting a damp problem in the lounge/bedroom?

Thanks,

Andy

 

[tell80]

You must be certain that there's only the one dormant flue - given there's only the one opening on the gable it should be simple enough to fit internal wall insulation to GF and FF gable walls?

 

[Nige F]

T

The only fireplace was downstairs and that's been all bricked up for about 7 years (so yep, I'd presume just one flue).

Given the age of the house - there will be no upstairs fireplace. The large outside chimney is a decorative feature.

 

[Andy.T]

Thanks both.

Yep I think you're right Nige. It was built in 1970 apparently, does that bear that out?

We could look at internal wall insulation, if that's the only way to do it. Both rooms have been decorated fairly recently though, so it would be a major pain.

Is insulating the chimney itself definitely a "no no" do you think?

It's just that I came across a few posts online (this one for example) where people talked about pouring insulation (poly beads or vermiculite) down from the top?

That sounds tempting/easy, but it does seem to go against everything I've heard about "always needing to allow the movement of air" in a redundant chimney?

That said, to my (admittedly fairly clueless) mind, it almost sounds like you'd just be turning the chimney into a big cavity wall? We don't worry about venting them so much do we? Presumably because they shouldn't be holding so much cold air?

Sorry for the rambling! I'm very confused and looking for a cheap effective solution, where perhaps one doesn't exist or isn't wise.

Andy

 

[tell80]

Forget about insulating your chimney breast or chimney flue - there will be some heat loss but not a significant amount.
The cost benefit of internal wall insulation would eventually pay back.
If the tile hanging is on a masonry outer skin then its fine but if the tile hanging is on a stud framing there could be a big heat loss?

 

[cdbe]

Even if you were to fill it with insulation, you're still faced with the thermal bridge of the brickwork interrupting the cavity. The only thing I would consider is insulating internally with two x 8x4 insulation backed plasterboard fixed with suitable adhesive (you can get 50mm or 62.5mm thick so there would be some projection into the rooms and a bit of (DIY) making good required. Personally with current energy prices I would either be doing this or opening up the fireplace to burn pallets!