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Connecting a 4" flue to a 5" stove?


jhodgski

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I (incorrectly) thought my flue had an OD of 5", so I've bought a 5.5KW multifuel stove with a 5" flue connection.

However, having now received the stove, I've realised my flue is approx. 4" OD.

In the paperwork that comes with the stove, I think it said that a 5" flue diameter is required for stoves up to 9KW. Given that my stove is only 5.5KW, would it be OK to connect my 4" flue to it?

If so, is there an adapter I can buy?

And can anyone advise on how to disconnect my flue from the collar that sits on the narrowboat roof? I can't see anything that needs untightening, but I cannot get it to budge. What is the knack to get the flue off? (Actually, I just need to rotate it a bit so the new stove can be positioned in the best place.) It's quite an old flue, though, so I need to be careful with it / not hit it too hard... :-/ :-)

Thanks,
James

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23 minutes ago, jhodgski said:

And can anyone advise on how to disconnect my flue from the collar that sits on the narrowboat roof? I can't see anything that needs untightening, but I cannot get it to budge.

They are normally held in with silicone and fire rope. Removal normally entails digging out the silicone from the collar. 

 

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I reckon your 4"flue would be fine, and you should be able to find an adapter to connect flue to fire.

The flue is only fixed in position by virtue of fire rope tamped into the gap between the flue and the collar, usually with some fire resistant  silicon, you need to work out the packing with knife, screwdriver etc whatever will do the job.

Phil 

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16 minutes ago, jhodgski said:

OK, thanks for the replies. Presumably, the rope/silicon is on the underside of the collar (rather than outside)?

Does anyone know the proper name for the adapter / where I can get one?

The silicone and rope is in the gap between flue pipe and collar. 

 

Flue pipe reducing socket /adaptor e. g

https://www.elyboatchandlers.com/solid-fuel-stove-hardware/flue-pipe-reduction-socket

Edited by rusty69
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When I had my Squirrel there was a 4" cast iron flue pipe which worked just fine.

The flue pipe had a joint socket formed on the end designed to accept the next bit of flue pipe. This fitted beautifully (upside down) into the 5" flue connection on the top of the Squirrel.

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1 minute ago, Mike the Boilerman said:

When I had my Squirrel there was a 4" cast iron flue pipe which worked just fine.

The flue pipe had a joint socket formed on the end designed to accept the next bit of flue pipe. This fitted beautifully (upside down) into the 5" flue connection on the top of the Squirrel.

Was it not a bit heavy for the wafer thin squirrel top plate? 

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Morso make a part specifically for the squirrel to reduce the 5" hole to fit a 4" pipe and a squirrel doesn't deliver 9Kw so I think your stove will be OK with a 4" pipe.

You might have a bad experience with the flue pipe and collar. On mine I pulled the whole lot out through the roof. Once the bolts that hold the collar to the roof are released the whole lot came out easily. I tapped the collar with a hammer to separate it from the pipe and it fell apart. Unfortunately it fell apart because it was wafer thin after 20 years of acid and corrosion. I have just cut it up to dispose of it and it is 4mm pipe in the middle but at the top it was as thick as Bacofoil. Incidentally I checked the new one from Midland Chandlers and the wall thickness is only 3mm. 

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Thanks for the latest replies.

I didn't measure up properly - my existing flue is actually 4.5" OD. Midland Chandlers had the socket adaptor I needed - https://www.midlandchandlers.co.uk/store/category/1882/product/hf-462.aspx . Approx. £20 inc. p&p, so have just ordered it. Thanks again.

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On 20/09/2017 at 19:35, jhodgski said:

OK, thanks for the replies. Presumably, the rope/silicon is on the underside of the collar (rather than outside)?

The fire rope goes between the flue and collar and high-temperature silicone goes on top to prevent water or tar seeping between. You can use a basic 300C Plumba Flue for the seal at the top, but if you're sealing the flue to the stove and you want to use silicone on top of the rope (rather than brittle fire cement) get some Envirograf which goes up to 1200C. It's obviously cheaper just to buy a single tube of Envirograf to do both jobs. Look on ebay.

Edited by blackrose
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Dont forget that you need to leave Envirograf for a few days to "go off", and it gives off a lot of smoke when you first light the stove and it warms up - open all the windows, be ready to make a sharp exit, turning the smoke alarms off as you go ......

Once it's done this once, it's sorted and doesnt do it again :)

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5 hours ago, Richard10002 said:

Dont forget that you need to leave Envirograf for a few days to "go off", and it gives off a lot of smoke when you first light the stove and it warms up - open all the windows, be ready to make a sharp exit, turning the smoke alarms off as you go ......

Once it's done this once, it's sorted and doesnt do it again :)

Just done ours. Was expecting lots of smoke. Got non 

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4 minutes ago, Richard10002 said:

I wonder if they've changed the formula? It cant be right that it smokes like it did. I've used it twice in 6 years and it smoked like a good 'un both times. Last time was a few years ago.

I have not used it before, but have had smoke before after painting the stove.Perhaps I didn't get it hot enough, but put plenty in there, heated it up fairly slowly at first.

 

It does say, for every 10mm of thickness, three days must be given to wait for the vapour to clear.

Edited by rusty69
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On 20/09/2017 at 21:28, Mike the Boilerman said:

When I had my Squirrel there was a 4" cast iron flue pipe which worked just fine.

The flue pipe had a joint socket formed on the end designed to accept the next bit of flue pipe. This fitted beautifully (upside down) into the 5" flue connection on the top of the Squirrel.

We have the exact same.

I don't think 24 years is bad service.

 

Daniel

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  • 2 weeks later...

Does anyone have any tips on how to separate the flue from the top collar? I've tried pulling, tapping and twisting the flue but all I've managed to do is put my back out...

I can't see any sign of a rope on either side but there does seem to be sealant on the top side. There is a fair amount of corrosion (top and bottom) which I've chipped out as much as I can.

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