A neighbour is planning to cut into his chimney breasts and fit rigid flue liners for his woodburner. I have never heard of this before, and thought a double-wall flexible stainless steel liner would be adequate. Does anyone have any knowledge or experience of this?

The Old House Handbook says stainless flexible liners last 10-15 years. I wouldn't mind having something more durable - but not if it's a lot of work. We are considering a small (5kW) wood burner for room heating only.

I worked on a job where the farmhouse chimney was lined with pumped refractory concrete that was poured in after forming the flue with an inflated 'sock'.
It was great and pinpointed what would have been potential air leaks in the masonry.
Take a look at the doc attached to this url
www.solidfuel.co.uk/pdfs/lining_old_chimneys.doc

Thanks everyone, incredible information!

Good to know 904 grade is available if we are worried about corrosion. But since we intend to burn wood only, it may be an unnecessary expense.

I will also investigate ali.gill's inflatable-sock/refractory concrete solution. The Old House Handbook advises against it, but then Hunt and Suhr take a hard line against anything involving cement, and most of us can't afford to be so purist. (I might mention this method to my neighbour before he sets about his bedrooms with an angle grinder.)

Loose-fill insulation around an SS flue will presumably give a better 'draw', and might prevent corrosive or inflammable compounds condensing in the flue. On the other hand you presumably miss out on a bit of heat that might otherwise have helped to warm upstairs rooms.

Next question: if we go for a stove with an exterior air intake, is there any reason why we shouldn't draw the air from the space below a suspended timber floor? We need a bit of extra ventilation down there.

Posted By: rhamduLoose-fill insulation around an SS flue will presumably give a better 'draw', and might prevent corrosive or inflammable compounds condensing in the flue. On the other hand you presumably miss out on a bit of heat that might otherwise have helped to warm upstairs rooms.

It's worth remembering that this additional heat is only available when the fire is burning. The rest of the time you'll be losing heat to the chimney. It's better to insulate it, seal it with a backdraught flap when not in use &, if possible, keep it outside the thermal envelope of the house.

David

We got into huge problems with insurers when we mentioned our log burner and thatch on the same form. They sent a "chimney engineer" who said that we needed our flue insulated along its complete length and a through draft from the house, up the outside of the chimney to an airbrick near the the top. This would have necessitated rebuilding the chimney and replacing the 904 lining we had installed 2 years previously. We then learned from our original installers that the upper 2/3rds of the flue are insulated, and the rest is in the void of a huge inglenook chimneyso there is no possibility of heat getting into the stonework. Indeed, we have a temperature sensor on the chimney in the loft, near to the thatch and it has never triggered (50c). Insurers said that this wasn't good enough. So we got two more opinions, both saying the current installation was ok, and even got sight of a HETAS report on chimney design that suggested that the airbrick in the flue idea could be a fire risk, and would be a source of major heat loss for the house. Still no joy from the insurers. In the end we found another insurer, who was happy with the fact it was lined and asked no other questions.
To conclude:
ask a dozen experts and you'll get a dozen opinions
insurers will always favour the most expensive / stupid solution