Which flue for a Hobbit
Could I fit a four-inch twin wall flue to a Hobbit stove and take the 6in external flue directly through a 6in cast collar? The insulated chimney would then continue the flue from the top of the collar. This would make installation within the boat much simpler because it would allow only a 60mm air gap between the twin wall flue and any combustibles.
ROGERSPURR, via the CB website
TONY REPLIES... The Hobbit SE is listed as having a 4in flue so that is fine at the bottom. I can see no reason you cannot fit the whole flue through a 6in roof collar, but with one important proviso. You will be leaving the top of the insulation between the two skins exposed so you need to seal it against water and tar ingress. I’d suggest high temperature silicon.
Be sure to always use a cap on the collar or fit a double skinned chimney. Make sure the inner skin of the chimney fits inside the 4in flue and fill the void between the inner skin and outer skins of the chimney with something like expanding foam so any condensation in the chimney drops into the stove rather than into the insulation.