Flue installation question

[DrGonzoMIA]

Just in regards to installing a flue through a roof collar. Should the flue pipe be cut flush with the top of the roof collar. And the the chimney be fit over the roof collar. Or should I take the flue pipe up to the same height as the top of the chimney ? Cheers

[Jen-in-Wellies]

5 minutes ago, DrGonzoMIA said:

Just in regards to installing a flue through a roof collar. Should the flue pipe be cut flush with the top of the roof collar. And the the chimney be fit over the roof collar. Or should I take the flue pipe up to the same height as the top of the chimney ? Cheers

Flush with, or slightly above the top of the collar. Definitely not to the same height as the chimney, or it will be destroyed by the next low bridge, or tunnel. The point of canal boat chimneys is that they are removable. Your location says Doncaster, so low bridges are not common, but cruise further away and you'll find them.

Use high temp silicone sealant between the collar and flue to give some compliance to prevent high forces being put on the stove top by the heat expansion of the pipe when it is hot.

Jen

Edited September 14, 2021 by Jen-in-Wellies

[Canal321]

Flush 

[dmr]

1 minute ago, Canal321 said:

Flush 

 

The bloke who did my flue (put the bends in) said its roughly a 50:50 split between those who like them flush with the top of the collar and those who like them protruding by a few mm. I have two stoves and one in each style, I prefer very slightly protruding.

[bizzard]

I'd make em protrude as much as possible, they rust and corrode from the top downwards. 

[blackrose]

44 minutes ago, DrGonzoMIA said:

Just in regards to installing a flue through a roof collar. Should the flue pipe be cut flush with the top of the roof collar. And the the chimney be fit over the roof collar. Or should I take the flue pipe up to the same height as the top of the chimney ? Cheers

 

Definitely no more than an inch higher. You should have a 1/4" expansion gap all the way around between the flue and collar. Stuff that gap with glass fire rope and put some high-temp silicone sealant on top of the glass rope to stop water or combustion residues seeping between. Envirograf is the best high-temp sealant I've used. Assuming your insulation is sprayfoam, have you removed 4 or 5" radius around the flue where it goes through the roof? The small area you've stripped of sprayfoam can be stuffed with rockwool, but not too tightly. 

[DrGonzoMIA]

Cheers all. It's a 6" roof collar and a 4" pipe that goes through (at a bit of an angle) I have a stainless pipe section so will do as you say and leave a couple of mm protruding. Mines not actually a narrowboat but a river cruiser jobby so I'm pretty screwed with bridges anyway 😅

[David Mack]

If you stop the flue pipe a little below the top of the collar, you can slope the silicone sealant down towards the flue, so that any condensate which runs down the inside of the chimney is more likely to find its way back down towards the fire. A projecting flue forces this to flow out across the roof instead.

[Jen-in-Wellies]

57 minutes ago, DrGonzoMIA said:

Cheers all. It's a 6" roof collar and a 4" pipe that goes through (at a bit of an angle) I have a stainless pipe section so will do as you say and leave a couple of mm protruding. Mines not actually a narrowboat but a river cruiser jobby so I'm pretty screwed with bridges anyway 😅

Important extra information! If it is a stainless pipe flue, then you can happily take it as high as the highest other part of your boat. No problem with it looking unsightly with rust. Any tar on the outside of the stainless tube can be removed with oven cleaner.

Jen

[blackrose]

1 hour ago, DrGonzoMIA said:

Cheers all. It's a 6" roof collar and a 4" pipe that goes through (at a bit of an angle) I have a stainless pipe section so will do as you say and leave a couple of mm protruding. Mines not actually a narrowboat but a river cruiser jobby so I'm pretty screwed with bridges anyway 😅

 

So a 1" gap between flue and collar? That's a big gap. Mine is about 3/4" and that's still bigger than recommended. Be sure to stuff plenty of the thickest fire rope you can find around it so that there's no physical movement at the top, otherwise the risk is that the flue moves at the top and the seal cracks at the bottom, on the stove, potentially allowing CO into the boat.

[DrGonzoMIA]

Sorry. I kinda confused the issue...internal diameter of roof collar is 5". I got hold of some decent 15mm rope which fits quite well. I like the idea of having the flue just short of the collar so the sealant can be banked down to try and direct moisture back into the flue to be burnt off instead of out and rotting the chimney base.

[blackrose]

That should be fine then.