We are in an end of terrace 1930s property

The gas fires we had in the downstairs front and back room have been removed, so now is an opportunity for me to insulate the chimney breasts

We share the top of the chimney (outside on the roof) with the neighbour on the party wall

I was assuming polystyrene beads shoved down the pots, or a chimney balloon shoved in from the gas fire position

But I've heard that the polystyrene beads may trap moisture

And for the balloon, surely all it does is stops drafts? Even though it's a party wall, you still have that whole chimney breast column of air, which must be transporting heat that passes from our rooms into the breast, and up out the chimney.

I thought maybe to cap off the top, and insulate the bottom, but I believe you are supposed to keep it ventilated right?

Many thanks

several threads on this:
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12110&page=1#Item_0
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12636&page=1#Item_0
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12432&page=1#Item_0
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=12110&page=1#Item_0
http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11226&page=1#Item_0

Consider getting rid of the chimney breast altogether. Otherwise, opinion seems to be seal and insulate above the heated envelope (in the loft if you don't have a heated attic), vent in the loft, ventilated cap on the pot. Whether you then want to fill the internal flue or not depends partly on what the neighbours have done with theirs - assuming theirs is open then you effectively have an external wall rather than a party wall adjoining a heated building, so you might want to insulate it. If you don't you probably want to vent top and bottom.

I've had a chimney balloon in my bungalow for 7 years. No problems and it reduces the draughts but does not eliminate them completely.

Right, well I think I've got the jist, and thanks for those links haplessDiyer

Tony, just finally to make sure I've understood correctly, can I ask:

Why is the airbrick in the loft is required if I have ventilator pots. Is it just a belt and braces approach?

And do I still need need an airbrick/vent at the bottom i.e. in my photo above, and how far off the floor?


A picture paints a 1000 words................

Nice pic!

loft insulation up to 400 above ceiling round chimney and beads up to same level 50mm below air brich, 150 ali louvre removable, check beads after a few months for settlement

no air brick needed at the bottom

I assume it's so that you get cross-ventilation of the unfilled upper part. One vent may not even result in much air getting in (same applies to sub-floors etc - see many other threads), and certainly won't encourage good 'scavenging' of w.v.


Is that your rationale, Tony?

Nick

That's great Tony. Thanks so much for your continued contributions. Experienced knowledge goes a long way.

Finally, I think all the above points refer to a chimney on an internal wall.

How does it differ with an external chimney. Is it just that you would need another airbrick at the bottom as you're likely to get more condensation problems since the chimney is colder?


Thanks

Ok, I just wanted to put together a little summary for anyone who comes across this post as it might be quite useful.

So here goes:


HEAT LOSS FROM A DISUSED CHIMNEY:

In the past when chimneys were used with fires, the stack effect would create draw, which naturally caused warm flue gases to flow up the chimney and out the chimney pots. Well now the same thing is happening as the whole height of the flue is heated from the ambient heat of the house which travels up and out the chimney pots due to the stack effect.
If you ever get the chance on a cold, still day, stand by a flue pot and you can easily feel the warm air rising from it - it's quite considerable.
Also, if you cover a fireplace with a thin piece of cardboard or metal, you will hear and see it flex as the wind blows across the chimney pot, clearly showing how easily air moves up and down the flue.


MINIMUM INSULATION:

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 Ă‚Âľ of heat loss through the flue. Note an airbrick/vent is not needed at the bottom of internal chimney.


RECOMMENDED INSULATION:

For most of the remaining Ă‚ÂĽ of energy (note: there would still be heat loss via the fabric of the chimney itself cold bridging), EPS beads, vermiculite, LECA, perlite or similar poured in through the airbrick in the attic helps reduce thermal thermal losses up the chimney flue and is easy to remove (note if a flue is still in use, polybeads may melt, whilst LECA is thermally more resistant).
Unless you keep the fire place open, the insulation sits on the fire slab if it gets bricked up. If you keep the fireplace open then a reasonable register plate keeps it all "up there".
Take loft insulation 400mm up chimney breast from ceiling below (50mm below airbrick), and bring insulation beads inside flue up to same level.


A NOTE ON SEALING OFF THE CHIMNEY WITHOUT VENTILATION:

If you just cap off the top and insulate the bottom, “pumping” will happen. This is when in an closed off chimney the top gets very cold, condensation occurs and the cold air falls down the chimney, warm moist air rises, this dries the chimney breasts and indeed the house but dumps water in the form of condensation in the top of the chimney, saturating it until it can take no more at which point it starts dripping, running down the flue. This is like a cold tropical rain forest and not good. Adding loose insulation fill however, will not affect pumping.



A NOTE ON AIRBRICKS:

Chimneys can act like dehumidifiers with or without air movement condensation id drawn to the coldest points, the pot and the flaunching and can rain or run down the flue. An air vent does not stop this but it stops it being so bad and then once the sun comes out and warms the loft (most days) the whole thing drys out with warmed dry air flowing up the flue. This isn’t covered in literature, but in reality happens a lot if not well ventilated)