Blocking off unused pre-cast flue

[Mike Atkinson]

Can anybody point me at any advice/regs regarding blocking off an unused pre-cast flue?

We inherited a centrally heated house with an additional gas fire in the lounge. However its supply was later capped off as the metal flue pipe in the loft was leaking. We frankly don't need the additional heat - the wall up the stairs was also worryingly hot if the fire was used - and now want to reclaim wall space by removing the essentially condemned fire and its surrounding fireplace. This isn't inset - it just butts against what I assume are the pre-cast flue blocks going up to the attic.

I'd live to squirt expanding foam up the bottom of the flue and then make good the wall, but I suspect that is insufficient ;-). What needs to be done? Does the old flue need to be vented at the bottom? If so, how lounge (wife!) friendly can this look? The other side of the bottom of the flue is in the cupboard under the stairs. If a vent is needed, could the requisite opening be there?

Do I have to remove the top of the old flue from the roof apex? Can it not be left?

Many thanks in advance for any advice!

Mike

[Andrew]

On 11/04/2016 12:19, Mike Atkinson wrote:
> Can anybody point me at any advice/regs regarding blocking off an unused pre-cast flue?
>

> Mike
>
Just remove the flexible pipe inside the loft (but it could be asbestos
cement) and shove some loft insulation inside the angled flue block in
the attic. If you are going to remove the false chimney breast in the
lounge (opens up the room nicely) then make sure the upstairs floor
joists aren't sitting on it (as mine were). If so you'll need to extend
them into the wall. Then you will need to hack off the projecting part
of the angled flue block behind the false chimney breast (that the fire
or backboiler connected to). If it is in a party wall then filling it up
with concrete will improve the sound insulation that you are diminishing
by removing the false chimney breast.

[Mike Atkinson]

On Monday, 11 April 2016 13:54:47 UTC+1, Andrew wrote:
> Just remove the flexible pipe inside the loft (but it could be asbestos
> cement) and shove some loft insulation inside the angled flue block in
> the attic.

Thanks. You think no ventilation is needed at the bottom end?

> If you are going to remove the false chimney breast in the
> lounge (opens up the room nicely) then

There isn't one! It's just a wall. Until I looked up pre-cast flues I thought this was some after-fit solution, but I guess this was in place from construction. In the lounge I have a normal wall, and although there is a mantelpiece and fireplace surround, both project from the wall and don't appear to be built-in or inset. Inset wouldn't be possible anyway - the wall is about as thick as a brick length; I don't believe there's any cavity as it's not thick enough.

[Andrew]

On 11/04/2016 14:36, Mike Atkinson wrote:
> On Monday, 11 April 2016 13:54:47 UTC+1, Andrew wrote:
>> Just remove the flexible pipe inside the loft (but it could be asbestos
>> cement) and shove some loft insulation inside the angled flue block in
>> the attic.
> Thanks. You think no ventilation is needed at the bottom end?

It was never used for coal or wood. Gas burns quite cleanly and the flue
blocks are on the inner leaf, so isolated from the weather. QED just
seal it at the bottom and plug with some thing vapour permeable at the
top, like a plug of rockwool.

>
>> If you are going to remove the false chimney breast in the
>> lounge (opens up the room nicely) then
> There isn't one! It's just a wall. Until I looked up pre-cast flues I thought this was some after-fi

You browser seems to be posting lines longer than 79 characters for some
reason. Thunderbird not happy, and sig may have vanished.

[Capitol]

IME single leaf flue blocks are only used for gas fires.

[Muddymike]

My Thunderbird is quite happy with it!

Mike

[Mike Atkinson]

On Monday, 11 April 2016 18:37:46 UTC+1, Andrew wrote:
>
> You browser seems to be posting lines longer than 79 characters for some
> reason. Thunderbird not happy, and sig may have vanished.

My apologies if this is the case. I confess I'd forgotten about
line limits from mu old Usenet days.
All my messages are now sent in the "new" Google groups
using Chrome. I've just been looking for any configurations
options, to no avail.

[Martin Bonner]

You have to type the line breaks by hand. It's tedious.

[sarah]

Did you do this as I’m looking to do the same? I’m wondering how much breeze blocks make up the fake chimney breast and how much there would be to remove?

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For full context, visit https://www.homeownershub.com/uk-diy/blocking-off-unused-pre-cast-flue-1121951-.htm

[Andrew]

On 30/03/2021 22:01, sarah wrote:
> Did you do this as I’m looking to do the same? I’m wondering how much
> breeze blocks make up the fake chimney breast and how much there would
> be to remove?
>

You are replying to a 4-year old post !.

Class 2 flue blocks are 4 inches deep, so just form part of the
inner leaf of a cavity wall. They are longer than a standard 18 inch
block and apart from the 45 degree starter block above the original
back boiler/fire you can just leave them in place. In the loft
there will (or could) be another 45 degree exit block that is connected
to a roof or ridge vent exit with typically asbestos-cement pipe,
though older properties might have galvanised piping. Just stuff
some rockwool into the 45-degree exit in the loft after removing any
flue pipe. The matching 45 degree block that is behind the false
chimney breast can just be bashed out and made good with normal
blockwork. Then you can dispose of the false chimney breast too,
though there is a possibility that it supported some of the flooring
joists (mine did). These will need extending into the main wall.

[Mike Atkinson]

Sarah, yes, this was done, but by a contractor as part of some larger work. Note we didn't have any false chimney breast - just a plain wall - so I'm afraid I can't advise further. Good luck!