How to completely seal chimneys the right way?

23 Sep 2016
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United Kingdom
Hi everyone :)

Our house is an early 1900s, 4 bedroom, semi detached. It has 3 chimney stacks, and 6 chimneys/fireplaces as follows:

1. Living room (stack 1) - open fire place
2. Bedroom above living room (stack 1) - plaster boarded over with air vent
3. Dining room (stack 2) - plaster boarded over with NO air vent
4. Bedroom above dining room (stack 2) open fire place
5. Kitchen (stack 3) - completely blocked off, I think with breeze blocks with NO air vent
6. Bedroom above kitchen (stack 3) - open fire place

We have no fires of any kind and do not intend to have any in the future. All the open fire places are decorative only. All 6 of the chimneys are open at the top, with no caps/cowls.

The problem is, small amounts of rain water are coming down into the open fire places, and I imagine into the blocked ones too. We are also losing a lot of warm air from the house which is being sucked up the chimneys via the open fire places.

So we want to completely block off all 6 chimneys to (a) stop water coming down and (b) stop the warm air escaping.

The advice we have had from a roofer who is a family friend is to remove the chimney pots (we don't want them any more and they are a bit wobbly so a danger in high winds), and seal all the stacks at the tops. Then also place 2 air bricks in each stack (one for each chimney).

Is this correct? What about the 2 chimneys that are blocked at the bottom (dining room and kitchen) - do these need vents putting in once the stacks have been sealed at the top? The last thing we want is a damp problem!

Any help is very much appreciated!
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There's a mass of information on exactly your questions if you research recent posts here & in the building forum - follow my back posts FWIW?

Briefly: all flues must have through ventilation - from bottom to top.
All flues (esp. redundant flues) should be swept & smoke tested.
Its easy to re-new the flaunching (the old flaunching will need renewing anyhow) and to re-set the chimney pots - then insert mushroom air vent terminals.

The redundant fire openings can be blocked and vented just inside the flue at the throating. But the flues must be vented.
Thanks for the reply Vinn.

So I'll get the roofer to remove the chimney pots, seal the openings at the top of the stacks and fit air bricks at the tops of all 6 flues. I then need to put internal vents in the dining room and kitchen chimney breasts? All others are ok to leave as they are because they are either open or vented already?

Putting a vent in the dining room chimney breast won't be a problem as it's just plasterboard over the old fireplace, but the kitchen one is going to be an issue. It's completely breeze blocked up and has kitchen units with granite tops fitted against it (done before we bought the house).

Any suggestions?

Really appreciate the help :)
No, thats not what I suggested.
The pots & flaunchings are removed, & the fresh flaunching has the pots set back into it.
Mushroom air vents are then inserted into the pots.

Keeping the pots allows for future options, & it will look traditional as a 1900's house should.

You obviously have to open up any blocked off fireplaces to sweep the flues.

Cutting a vent into a "board" and fixing the board up the flue at the throating creates venting, a barrier to any debris, & allows the fire place appearance, and any appliance to remain in place.
The board cannot be seen.

The kitchen c/breast could possibly be vented from the back wall of the c/breast?
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Thanks Vinn.

Venting the kitchen flue externally is a great idea!

The 3 blocked up fire places cannot be opened to be sweeped as they are plastered over and decorated. Sorry of it's a silly question, buy why do they need to be sweeped?
Soot will attract moisture which will turn into hygroscopic salts that will work through the c/breast brickwork to appear on the decorated surface as staining and damp.
Sweeping is not enough, the flue must, as above, have through ventilation.

I understand that it can be a nuisance opening up finished surfaces but in the long run it will pay.
Thanks again for your help, it's much appreciated.

Opening up 3 of the fireplaces to sweep the flues really isn't an option at all.I'd guess that none of the flues have ever been swept before and there doesn't appear to be any staining or damp on the chimney breasts, also 2 of them have been sealed with no venting at the bottom for God knows how long. I'll make sure all 6 flues are vented at both the tops and the bottoms and hope for the best.

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