Morso flue - where to get pipe and what size ?

[jonathanA]

probably been asked many times before couldn't easily find a previous topic covering my question.

our boat has the ubiquitous Morso squirrel and unusually (compared to a quite a few other installations I've seen anyway) a straight 4.5" flue from the top of the stove to the usual deck fitting (not angled). no bends or offsets or funny welded angles just a straight pipe.  The morso flue collar appears to be 6" diameter, with a 5" sleeve then the 4.5" pipe, same into the deck fitting/chimney base thing.  Over the winter water has been seeping in and running down the flue, not a huge amount but enough to be annoying (we are not liveaboard).  I'm guessing that a combination of a bit of rust and failing sealant on the deck (roof) fitting is responsible (its not coming down the chimney because it happens when the chimney is capped.) so this fitting is probably going to have to come off and be sorted.

So whilst I'm at it I'm wondering whether to replace the flue pipe which is showing some signs of its age with a new piece and that might as well be 5".  The question is where would I get 5 foot or so of 5" diameter pipe. I know I can get lots of nice enameled stove pipes in 1m lengths from just about any stove supplier, are these ok for NB use ?

just to add the Morso twin wall flue kit at between £450 and £600 depending on supplier seems to be overkill and my northern upbringing is struggling with spending that sort of money on a flue.

any advice or guidance gratefully received.

[Jen-in-Wellies]

Midland Swindlers will sell you a suitable length of plain steel pipe. Can be cut to length with a jig saw, or angry grinder with a cutting disk. Fluegas is quite acidic and well corrode its way through the flue eventually. You may get away with just digging out the old sealant between the collar and flue at the top and resealing. Most likely this is the path that the rusty gunk is taking via the sealant. Check the end of the pipe at the collar with the sealant removed. That is where mine was corroded away when I had to replace mine. High temperature silicone for the roof collar, fire cement for the collar on the stove. You need the flex that the silicone gives at one end.

Jen

Edited January 22, 2018 by Jen-in-Wellies

[Jen-in-Wellies]

Just to add. The maximum diameter of a straight flue pipe like yours will depend on the angle at which it goes through the roof collar. The greater the angle, the smaller the pipe that will fit without hitting the sides at top and bottom. Something to check on the existing pipe once the sealant is removed. This is the reason for many NB flues having welded bends as it allows a larger diameter pipe to fit through the collar. If it is touching, or very close, then the sealant can't fit and it is a route for tar and gunk to get through. The roof is at an angle and the collar tube is at an angle to the baseplate as well. The flue will also probably be at an angle from the stove and all these angles are likely different, so looking to see what the gaps are at the collar is the only way to check if a bigger, or smaller pipe is needed. Changing flue pipe diameter also affects the draw of the fire, so be careful making a change. If you do want to use a larger diameter pipe then it may well need one, or two bends put in. Bends welded in will preclude enameled pipe, which is why you don't often see it used on NB's compared with plain steel with blacking.

Jen

Edited January 23, 2018 by Jen-in-Wellies

[BEngo]

Buy the pipe from a local steel stockholder. 115mm  ( 114.3 precisely)  Outside Diameter  Mild Steel  CHS ( Circular hollow section) is the stuff and available in up to 6.3 mm thick. I expect it will be as cheap to buy 3 pieces 2m long as as it is to buy one thinnest possible size bit from MC.  The next size up from 115 is 140 mm so no 5 inch equivalent.

N

[Cheshire cat]

If you were to buy 6.3 mm wall thickness it would be pretty heavy. My old one was 4mm and lasted 20 years. New one from MC turned out to be 3mm wall thickness.

[jonathanA]

Thanks Jen

Appreciate the detailed advice, you are right about the angles at the roof end for sure, something I want to check out during the dismantling process. I thought increasing the diameter would improve the draw but that’s never been a problem anyway but hadnt considered whether it might cause a problem lining everything up. Unless I can find some cheap 5” pipe i think I’ll stick with the same 4.5 inch stuff.

Thanks Bengo I spotted some CHS on a local steel stockholders website but wasn’t sure if that was the right stuff to use.  

[mrsmelly]

As others have said there are options. I always buy my stuff from Limekiln they do what you want at a good price delivered next day. Twin wall is an unneccesary expensive nonsense

[SweetPromise]

Hi all,

 

Just had a good read through this thread as it's basically the same as the questions I had. So that was really useful, thanks.

 

One more question to add, I've found a new 5ft chimney pipe for my morso squirrel 1410, and it's in 4.5" or 4". I believe I need 4.5" as I measured the rusty broken one that's here, but I also need to replace the chimney collar (also corroded and cracked, and finally accidentally cut with an angle grinder in trying to get the fused, corroded bits apart). On this website, it has a 5" and a 6" one, but both say they're suitable for a 4" diameter pipe... So does that mean I need to get the 4" pipe, and will that be ok with my morso, or will the 6" collar take the 4.5" pipe?!

 

https://www.chandlerydirect.com/chandlery-store-uk/flues-cowls-boat-chandlery-store.html

 

Thanks!

[BEngo]

The standard Morso Squirrel collar accepts 113 mm dia pipe with room for some fire rope and a good layer of heat resistant sealant.

 

The best places to buy a new collar are Harworth heating or more direct.

 

N

[Arthur Marshall]

Sealant or fire cement to fix the collar on the stove itself? I used cement and it does seem to be leaking. I was going to use sealant this time but not sure it will take the temperature.

[BEngo]

33 minutes ago, Arthur Marshall said:

Sealant or fire cement to fix the collar on the stove itself? I used cement and it does seem to be leaking. I was going to use sealant this time but not sure it will take the temperature.

Plumba flue survives on my Squirrel, but Envirograf has a really high temperature rating - 1200 C I think.  That is past red hot and it will be much better than fire cement which always cracks. Available from Amazon, about £14.

[MtB]

On 23/01/2018 at 22:38, mrsmelly said:

Twin wall is an unneccesary expensive nonsense

 

 

Except for one major advantage. 

 

You can expect it not to corrode through in six or seven years like the Midland Chandlers mild steel pipe I used on my Boatman stove. 

 

 

[mrsmelly]

Just now, MtB said:

 

 

Except for one major advantage. 

 

You can expect it not to corrode through in six or seven years like the Midland Chandlers mild steel pipe I used on my Boatman stove. 

 

 

True, though I never got even six years with mine lol.

[MtB]

Just now, mrsmelly said:

True, though I never got even six years with mine lol.

 

 

On the other hand the 1/4" wall thickness cast iron flue pipe on the preceding Squirrel lasted 25 years, and was good as new when the Squirrel fell to bits! 

[mrsmelly]

1 minute ago, MtB said:

 

 

On the other hand the 1/4" wall thickness cast iron flue pipe on the preceding Squirrel lasted 25 years, and was good as new when the Squirrel fell to bits! 

Yep, they were great, but unobtainable on later boats 

[Tracy D'arth]

19 minutes ago, BEngo said:

Plumba flue survives on my Squirrel, but Envirograf has a really high temperature rating - 1200 C I think.  That is past red hot and it will be much better than fire cement which always cracks. Available from Amazon, about £14.

Fire cement in the collar is the reason that they crack. Use Envirograf  over a turn of glass fibre rope.

[ditchcrawler]

How about stainless steel as used in chimney liners. 

 

 

[ditchcrawler]

6 minutes ago, ditchcrawler said:

How about stainless steel as used in chimney liners. 

 

 

NB SCH 10 Grade 316 Welded Stainless Steel Nominal Bore Pipe ANY SIZE OR LENGTH | eBay

 

[BEngo]

Good if you want a straight flue, but a bugger to weld properly if you need any bends.  Not so much the actual welding but the post-weld heat treatment.  Without this the life  of the pipe will be short where the weld heat has affected the stainless structure.

 

N

[BEngo]

I have been looking a bit more into 316 stainless  as a flue.  It apparently suffers from stress corrosion cracking above 60C, which is not ideal for a rolled pipe used as a flue.  It also suffers pitting corrosion and crevice corrosion when 'warm' chlorides are present.  Again, not what you want in a solid fuel flue.

 

Polish it up and it would look nice, for a while at least.

 

  You might get better results with the variant  316Ti, but that is likely to be pricey 

N

[ditchcrawler]

25 minutes ago, BEngo said:

I have been looking a bit more into 316 stainless  as a flue.  It apparently suffers from stress corrosion cracking above 60C, which is not ideal for a rolled pipe used as a flue.  It also suffers pitting corrosion and crevice corrosion when 'warm' chlorides are present.  Again, not what you want in a solid fuel flue.

 

Polish it up and it would look nice, for a while at least.

 

  You might get better results with the variant  316Ti, but that is likely to be pricey 

N

I wonder what grade my chimney liner is at home, thats ridged about 6 foot sections been in the house for about 30 years

[MtB]

11 hours ago, BEngo said:

I have been looking a bit more into 316 stainless  as a flue.  It apparently suffers from stress corrosion cracking above 60C, which is not ideal for a rolled pipe used as a flue.  It also suffers pitting corrosion and crevice corrosion when 'warm' chlorides are present.  Again, not what you want in a solid fuel flue.

 

Polish it up and it would look nice, for a while at least.

 

  You might get better results with the variant  316Ti, but that is likely to be pricey 

N

 

 

I've just had a stove fitted in my hovel. The (hefty) flexible flue liner they put in is stainless steel and specifically designed for solid fuel flue. I dunno what grade of stainless it is but I would imagine it is resistant to the pitting and corrosion you mention. 

[BEngo]

1 hour ago, MtB said:

I dunno what grade of stainless it is but I would imagine it is resistant to the pitting and corrosion you mention. 

One would hope so!  The trouble with stainless is that there are an awful lot of varieties and sub-varieties unto a couple of generations.  One of them is almost bound to do what you want, but finding it needs an expert.  Talking to specialist stockholders is OK, but they usually want to sell tons of steel  especially if they have to order it in. 

 

A 2m long bespoke flue pipe doesn't really cut it.😊

 

N