Q&A: Fitting a stove flue in a wooden-structure canal boat
PUBLISHED: 18:14 03 February 2021 | UPDATED: 10:01 04 February 2021
Christine Bird 2019
Our narrow boat has a wooden structure; can I still fit a stove in a wooden structure and is there a roof collar available for a 5” flue?
As our narrowboat has a wooden superstructure, I am trying to find out as much as possible about fitting a stove. Our stove has a 5 inch (125mm) flue and I have yet to find a collar with a big enough ID to take this, so I am trying to see what solutions others have come up with, if any! The boat was originally a Butty, built in 1935 by Harland and Wolff and has, as such, been much modified!
TONY REPLIES: There is a British Standard for fitting stoves in boats. See BS 8511:2010. Although not yet mandatory insurance wise, it would be a good idea to comply with it. Nothing I say below can be taken as overriding BS 8511, but is given as non-specific general guidance.
I was sure that roof collars suitable for a 5ins OD flue were available and a quick Google brought this up and Limekiln Chandlers also list them. You can also get reducers so you can use a smaller diameter flue, but you need to check with the stove manufacturer if this is acceptable. The roof collar on my metal boat never got hot enough to discolour the paint, so I think one will be fine on a wooden roof. Just make sure the hole you cut to accept it is maybe half an inch larger than the downward projection on the roof collar so the roof edge does not touch the collar boss, although I very much doubt anything untoward would occur if it did. The outside roof collar has a large outer surface area so it will radiate and conduct heat to the air and thereby stay cooler than a lot of the flue pipe.
I am more concerned about the internal woodwork like the deckhead/ceiling. If there is a gap between it and the roof then any flammable insulation around the flue needs removing and replacing with something non-flammable like rock wool. It is vital that the ceiling comes nowhere near the flue, so usually a ceiling trim is fitted that hides the oversize hole where the flue passes through the ceiling, but a quick Google did not find any decorative ones suitable for a 5 inch flue. I made my own rectangular one from a suitable non-combustible and semi-insulating fire board and painted it black with stove paint.
On a boat that age, the stove surround is likely to be ceramic tiles on plywood. This is unsafe because there have been cases where heat from the stove running hard has actually ignited the plywood backing. Nowadays, the surround should be metal or tiles over a fire board backing with an air-gap between the fire board and any wood that is behind it. It is also VITAL that you observe the gap between stove and surround as per that British Standard.