Chimney and collar alignment

[madsunday]

Only just got my boat and in the process of figuring everything out! 

 

Just got a chimney to fit my 6 inch collar. The outside fits over perfectly but the inside pipe doesnt line up even remotely close. I'm guessing they are meant to?

 

Has it just been set up wonky and I need to get a simpler chimney without a second internal bit?

 

Photo is looking down the inside of the chimney.

 

[blackrose]

I don't know if your picture looks any clearer on a computer screen but I can't really tell much about alignment from the image on my phone. As long as the chimney fits snugly onto the collar it will function as it should. 

 

Are you just referring to about how it looks from outside and it's not straight? A curved roof can do that but it doesn't really make any difference to how it works. Maybe a picture from outside would explain it better.

[madsunday]

It's got an outer tube and an inner tube.

 

So the outside fits fine, snug around the outside of the collar but the inner tube (which looks like it should fit down the hole into the boat) doesnt line up with the actual hole and stops the whole chimney sliding down fully onto the chimney

 

Hope that makes sense.  So the photo is looking down the centre of the inner chimney. And you can see how misaligned it is with the hole into the boat

[blackrose]

Yes I've got it now, thanks for the additional explanation.

 

It's not ideal. Is there and way to bend the inner tube away from the outer tube to give it the clearance you need to get it around the flue? It would then act like a spring and actually hold onto the collar really well. You should put the part of the inner tube that currently doesn't fit around the collar first if that makes sense.

 

If not you might need to think about getting yourself some tin snips and seeing if you can cut away a small arc of the inner tube to get it to fit properly.

Edited August 4, 2020 by blackrose

[dmr]

So is it the double skinned chimney or the flue in the collar that is wrong (eccentric)?   Or maybe a bit of both?  You need to find which component is wrong so you/we know what to fix. If you want us to decide (?) then take a photo looking square on up the bottom of the chimney, and square on looking down on the flue/collar.

 

Maybe the flue extends a bit above the collar and is set at an angle to the collar so that the flue top is not not concentric?

 

.................Dave

[blackrose]

I've never had one but never imagined the inner and outer tubes of double skinned chimneys were fixed together that well so would be a bit more flexible in relation to one another? Clearly not.

[Cheshire cat]

The inner should go inside the collar so that any tar drains back down the flue. With the current scenario burning wood will result in tar emerging from the outer skin and staining the roof of your boat.

[Tracy D'arth]

Its not considered essential that the inner fits in the flue pipe.

The inner is sealed to the outer of the chimney at the top so heat and fumes go up the inner 'cos they can't get out any other way.

Any condensation and tar should drip down into flue pipe  not run down the outer to stain the roof.

 

If you are lucky.

[madsunday]

Done some playing around. No way it's going to bend or move into place, credit where it's due its rock solid. Rather than try and cut the inner one short I will change it for a single skin 

 

Thanks all for the input

[Tony Brooks]

25 minutes ago, madsunday said:

Done some playing around. No way it's going to bend or move into place, credit where it's due its rock solid. Rather than try and cut the inner one short I will change it for a single skin 

 

Thanks all for the input

Only do that if you like cleaning tar off your roof and cabin side.

 

I am with Cheshire cat, ideally the inner pipe should go into the stove flue and if it won't bend so it does, It only needs to be a mm or two. Then fill the void around it with expanding foam or crushed up kitchen foil so the hot gasses can't condense on the outer chimney skin. Don't totally fill it, leave enough space to push it over the roof collar.

[ditchcrawler]

You can buy inners for them https://smokiejoes.co.uk/product/narrowboat-chimney-liner    https://www.jonesboatchandlery.co.uk/stainless-steel-narrowboat-chimney-liner  https://www.midlandchandlers.co.uk/products/stainless-steel-flexi-chimney-liner-18-ch-092

[Cheshire cat]

I didn't explain well enough. In the situation where there is misalignment the fumes will go up the inner liner but some of them will condense on the inner liner surface. Because of the misalignment they won't all fall back down the chimney, some of them will hit the collar and then run sideways, eventually emerging from under the bottom of the outer. 

 

This will also happen if you have a single skin chimney with a hat on and you burn wood. It's impossible to get a water tight seal between the chimney and the collar and be able to remove it when the need arises.

[dor]

I had one of these double-skinned chimneys and the inner didn't fit tightly in the top of the flue, although it did go into it. and although the outer was a good fit around the collar some smoke would go up between the two skins and  I still got some condensate on the roof.

 

I have finished up with a length of steel tube (4"OD) that fits snugly in the top of the flue.  I've rivetted a chamfered band round the chimney about three inches up to provide some sort of seal and prevent the chimney dropping down the flue.

Easy to remove when leaving the boat and no condensate on the roof.

[BWM]

The interior flue pipe is most likely to be installed off centre in the collar and unable to line up, depending on how the liner is attached to the chimney it may be possible to adjust it by putting a scaffold pole or similar into the liner whilst someone holds the chimney and move it a little. Once you have changed the angle, rotate it around the collar and it should drop in to place.

[dmr]

The chimney inner does not need to be a snug fit in the flue, it can even be a bit above the flue, as long as its within the diameter of the flue any condensate should mostly fall back into the flue to be reheated and expelled rather than making a messy mess on the boat roof.....and eventually down the cabin side.  Very little fumes will go up between the chimney skins as they are sealed at the top so nowhere to go. Some people fill the gap between inner and outer skins with high temperature insulating fibres to get the inner hotter to improve chimney draw. I would say this does help a bit with the longer chimneys but is not an obvious improvement with shorter chimneys....but it must help a bit.

 

...............Dave

[Tony Brooks]

1 hour ago, dor said:

I had one of these double-skinned chimneys and the inner didn't fit tightly in the top of the flue, although it did go into it. and although the outer was a good fit around the collar some smoke would go up between the two skins and  I still got some condensate on the roof.

 

 

That's why its a good idea to fill the void between the inner and outer skins with foam or some such.

[madsunday]

Just incase its clearer, this shows how 'not central' the hole is... 

 

Also I know its rusty as hell... it's on the list

[blackrose]

18 hours ago, Tony Brooks said:

Only do that if you like cleaning tar off your roof and cabin side.

 

 

I think we're generalising a bit here. My chimney is single skinned and I don't get tar on the roof or cabin side.

[dor]

3 hours ago, madsunday said:

Just incase its clearer, this shows how 'not central' the hole is... 

 

Also I know its rusty as hell... it's on the list

Well that explains why the chimney cone is out of alignment!

It might be possible to remove much of that silicone, centralise the flue and re-silicone it.  Use fire rope to hold the flue in position then use a high temperature silicone to seal, e.g. 'Delta'.  It doesn't need to be as heat resistant as that used on the collar as it doesn't get that hot.  Using silicone allows the flue to move a little to accommodate expansion, otherwise it can crack the top of the stove.

[Tony Brooks]

1 hour ago, dor said:

Well that explains why the chimney cone is out of alignment!

It might be possible to remove much of that silicone, centralise the flue and re-silicone it.  Use fire rope to hold the flue in position then use a high temperature silicone to seal, e.g. 'Delta'.  It doesn't need to be as heat resistant as that used on the collar as it doesn't get that hot.  Using silicone allows the flue to move a little to accommodate expansion, otherwise it can crack the top of the stove.

 

I bet it won't be. I suspect the flue is set at an angle to avoid getting the flue "dog legged".

3 hours ago, blackrose said:

I think we're generalising a bit here. My chimney is single skinned and I don't get tar on the roof or cabin side.

Well aren't you lucky. It may also be that you burn fuel that produces minimal tar. I suggest that you are taking experience of just one boat and applying it to all and that is not very helpful. Even with insulated twin skinned chimneys you can get tar on the roof in really cold weather.

[Tony Brooks]

I think it would still be worthwhile trying to bend or reposition the inner skin the enter the flue, as someone said maybe drill out a couple of rivets so the inner can move around. Fit it while manipulating the inner via the top to enter the flue and then re-drill and re-rivet the inner.