Hi

I have been searching on this forum for advice on sealing up / insulating my chimney. I've found a really good thread from 2014, but obviously I'm about 8 years late to add to the thread.

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12781

In the above there's a post from JT101 who helpfully pulled together various other threads and summarised the best way of 'minimally' insulating your chimney as follows:

Put a ventilated rain cowl/cap on the chimney pots.
Now plug the bottom of the flue with a chimney balloon or similar.
Ventilate the top part of the chimney e.g. in a cold attic 450mm up from the ceiling below it. Remove a brick or two and replace with an airbrick or aluminium louvre.
This will prevent ¾ of heat loss through the flue. Note an airbrick/vent is not needed at the bottom of internal chimney.


My house is a late-victorian mid-terrace that has a full length cellar, an originally-converted attic and two chimney breasts with five flues in total. Of the five flues, two have been sealed at room level for maybe 30-40 years. The other 3 are unused (so I don't have any heating appliances in them) but are unsealed at room level.

I was thinking of plugging the bottom of the open flues with a metal plate that has a cleaning hatch in it so I can clear out the 'parge' that falls down every so often. My thoughts are a metal plate would be better than just 'shoving a chimney balloon' up there and hoping it seals well, but not as much work to undo as bricking the flue up.

Has anyone got any experiences of installing a plate as opposed to just going with a balloon?

If you seal at the bottom and vent at the top all the chimney breasts in the house are effectively uninsulated outside walls even if the chimneys are between neighbouring houses.

If you want to minimise heat loss Id sweep the chimneys to get most of the loose soot/mortar out, seal at the bottom to stop dust entering the room then either-
1 draught seal at first floor ceiling level and add insulation over the sealing plate and 500mm up the inside and outside of the chimney walls to reduce cold bridging. This could give you a warm chimney but still potentially have heat loss to the neighbours or outside if the chimney is on an external wall.
2 draught seal at the bottom and full fill the chimney with polystrene beads or vermiculite to 500mm above first floor ceiling level. Insulate the outside of the chimney for 500 mm above first floor ceiling level to minimise cold bridging.

Lots of grotty work but with 5 uninsulated chimneys in the house, Id guess youre loosing lots of heat at the moment

This is the view from underneath...

So here's some more info I left out.

- I don't share any of my chimneys with my neighbours so my chimneys just back onto the party wall.

- My attic has an original conversion so is fully floorboarded except in the eaves. The only insulation under the floor is in the eaves where there's rockwool batts.

The good news is I'm hoping to get a reroof this year and plan to insulate the attic to current regs and put heating in there.

So my query really relates to the situation where the attic is a 'warm' room.

Phil - If I make the attic a warm room, how would that affect your advice?

Posted By: lsxSo here's some more info I left out.

- I don't share any of my chimneys with my neighbours so my chimneys just back onto the party wall.

Phil - If I make the attic a warm room, how would that affect your advice?

You may not share the flue with your neighbours but heat can flow through an uninsulated chimney structure from you to them or vice versa depending on which building is the warmer. Being a victorian terrace the party wall is almost certainly solid with no insulation.

Think of the chimney as a cold tube where any heat that gets into the chimney will rise to the top of the tube and be lost to atmosphere. A rain cap wont stop heat loss. If you insulate the room in the loft but do nothing with the chimneys youll still have 5 very efficient convectors ferrying heat to the top of the chimney and off to atmosphere.

As Tony suggested, take them down when reroofing

No glue needed on beads, fill to level of loft insulation 500mm

Removed brick just above that

Re party wall. I have these on my list of ‘in-house winter cooling systems” cold air and wind cools both homes and when not windy heat I’d converted away up the cavity, sometimes the cavity turns into a 9” solid wall in the loft - I would fill the party wall cavity if it was mine

Top no sealant, even no plate, cardboard or newspaper

Bottom, seal with acrylic sealant, not sure I suggested plastic but it would work

Hi Tony, re: insulating outside chimney at loft level to 500mm, I take it that is a vertical measurement from topside of ceiling? I already have about 230mm loft insulation, so I take it I top it up around chimney by 270mm but how deep horizontally( out from chimney) do you know?
Also, you don’t happen to know what the linear thermal transmittance of this solution’s thermal bridge would be do you? (I’m modelling my house in PHPP for fun.)