How to connect steel liner to boiler pipe

[Peter Scott]

I have been putting off this job for a long time!!!

I have an oil-fired boiler that exhausts into socketted steel pipes of about 9cm diameter. They rise at an angle then disappear into an adjoining chimney breast. I know from watching the builders at work that the chimney stack has a brown ceramic liner. It has quite a large but unknown diameter.

Condensation is causing staining on the chimney breast and the chimney breast goes through a bedroom upstairs that gets too hot.

For all these reasons I want to line the chimney with a flexible stainless liner. I know how to do the roof bit as I have a scaffold tower and roof ladder. However I have no idea how to connect the liner to the existing pipes. I also believe that a moisture trap can be fitted.

Has anyone done such a job? Should I replace the pipes rising from the boiler to make the connection easier? Can anyone recommend a supplier or an information site?

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Peter Scott

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[John]

I had to "fix" a similar problem last year. The oil boiler was a Firebird which had two flue size options (4" and 5" with a stepped spigot for simplicity). The installer had simply shoved it under the exisiting 5" pipe which set off for the first 1.5 metres in stove enamel steel then changed to embedded asbestos cement through the house and out of the roof. We dropped a 4" liner straight down the old flue and sealed it to the boiler spigot with good fire cement. At the top we used thick fibreglass rope wrapped around the liner to close the annulus between old and new and sealed with mortar before replacing the O-H cowl. This stopped the problem entirely as- a) the single unjointed length of liner had no joints to let condensation out but more importantly- b) condensation was avoided as the thin liner within an enclosed space warmed rapidly in use thus no cold masonary or chilled metal was in contact with the flue gases to cause water vapour to condense. c) If there is room for it you can fill the annulus with vermiculite insulation chippings which while not absolutely esential is a very "good thing".

[Peter Scott]

Very interesting. I hadn't realised that the liner would prevent the condensation. What you say makes a lot of sense. Any damp will go as soon as the boiler fires and heats it up.

I like the idea of the vermiculite. That would definitely solve the room heating problem. Belt and braces.

It sounds as though you took the liner right down to the boiler? I would prefer not to see the liner if possible and to seal it to the existing steel flue pipes (or replacements if I have to). Any thoughts? Or perhaps someone else has done this?

Thanks John for your very helpful info. Out with the scaffold as soon as the weather improves. Or are we at the start of Day After Tomorrow?

Peter Scott

[John]

Yes the liner went inside the stove enamel section. It would have been ok to simply connect the liner into the top of the stove enamel section using fibreglass rope caulked in with fire cement but the exposed length is a source of cooling so should be kept within a limited length of say 1 to 1.5 metres. Alternatively a section of twin wall pipe could be used for the exposed section. Exposed to view liner is really a no-no. It might be possible to take the liner down to the boiler and then lag it and wrap with a thin aluminium casing so as to become virtually a piece of Selkirk SM if you cannot thread the liner through the stove enamel tube