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Chimneys & Fireplaces

Chimney leaking smoke/gases into cavity wall - solutions?

I recently had my gas fire serviced. As part of this a smoke test was performed to check that the chimney was working correctly. Whilst smoke was seen properly venting from the top of the chimney to the outside, the engineer detected some "backdraft" which caused him to check the loft space. Upon checking we could see smoke venting into the loft space.

I understand that I have a class 2 flue, which I believe means this is a 5 inch, precast flue, which is built into the internal wall of the house during construction. The house was built around the early 90s. There is a metal pipe in the loft from the top of the cavity wall, leading up to a vent ridge tile.

The engineer checked the metal pipe and believed there is no smoke leakage from this. He believes the smoke was leaking from the pre-cast flue at some point within the cavity wall, and travelling up, and venting from the cavity wall into the loft space.

As a result the engineer has condemned the chimney, stating that it is unsafe, because there is the possibility of carbon monoxide build up in the loft space, which could seep back down into the house. He has therefore disconnected my gas fire from the gas supply and attached a warning/unsafe notice.

I would like advice on my options here. I know I could have an electic fire installed, but this would be my last resort, since I have no wiring readily accessible.

The engineer claimed that the only solution would be to have the internal walls of the house ripped out along the length of the chimney, to find where the leakage is originating from, and repair it. I have ruled this out due to the sheer cost and scale of damage it would cause.

I did ask about the possibility of having the chimney lined, but the engineer claimed this is not possible with class 2 / pre-cast flues. However, researching on the internet it certainly seems that liners are available for class 2 flues. I would like advice from others as to whether this is a possibility, and if so, the rough cost to install.

I know there are flue-less gas fires available but I have been discouraged from these since they cause condensation and require a vent.

If the flue liner is not a possibility I would appreciate any other suggestions as to how to resolve my problem. I would really like to have a working gas fire again.

1 Answer from a MyBuilder Chimney & Fireplace Specialist

Best Answer

Very much depends on the type of class II flue that you have. Impossible to say without looking at it. There are class II liners available of course but if you already have a 5" diameter sectional flue it would not be possible to get a 5" liner to pass through it.

Look at a company called eldfast. They have a system which can put a very thin coating on the inside of your existing liners which will seal them but maintain the required cross section to keep the chimney working.

Martyn Heywood.

Chimney Care & Repair.


Answered 17th Dec 2012

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