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Double skinned chimney's

I am planning a few boat jobs for the spring and,having spent part of last year sorting out the wood burner, I wondered if it was advantageous to fill the cavity between the inner and outer skin of a double skinned chimney. I have searched online and various people have filled the cavity with fire resistant foam, rockwool, or tin foil and others say there is nothing to gain.

Asked by: Andy Hunter  | 4.50pm, Friday 16 March


WW says:

The only real advantage would be to reduce the external temperature of the chimney: the flue length is so short that it won't have much impact on the draw of the stove.
One potential disadvantage is that it might overly secure the chimney to the collar; hitting a branch (or bridge!) might then distort the cabin top, rather than the chimney being lost!
However, if you can fit a double-skin chimney, so that the inner lining fits inside the flue pipe (rather than fitting to the outside) you will gain an advantage of any tar products being sent back down the flue to be combusted, rather than staining the outside of the cabin top. Just ensure that it does not restrict the flue.

Mark Langley  | 10.22AM, Monday 19 March

Is your chimney the type that has an extra piece of tapered tubing that fits inside the collar whilst the main chimney fits around the roof collar?
Burning carbon based fuel creates moisture that will condense inside a cool chimney outside the boat. This washes tar and smoke deposits off the inside of the chimney. A tapered inner liner will direct this water and tar back down the flue to be evaporated again, rather than causing black marks on the cabin top.
The new British Standard (BS8511:2010) advocates the use of insulated flue pipe, collar, and external chimney which will improve the draw. This is usually made from stainless steel tubing with glass fibre wool or vermiculite insulation between the two skins. Insulating your chimney void with glass fibre wool will give a small improvement, however the effect will probably be too small to measure.

Rupert Smedley  | 12.41PM, Monday 19 March

I do not see any problem, however I do not think you will see any difference in the stove operation. If however I am proved wrong do please let us know!

Rupert Smedley  | 1.50PM, Tuesday 20 March


Readers say:

Thanks very much for the comprehensive answers. I am rather favouring a fire rated expanding foam option. Would this be ok?

Andy Hunter  | 8.36PM, Monday 19 March

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