Flue Sizes

[Martin_B]

I'm about to install a new Morso Squirrel stove but have stalled as I thought I knew what I was doing until I asked a daft question - flue pipe diameter. The top collar on my stove has an inner diameter of 135mm which I expect is correct for using a 5" (125mm ) vitreous enamel pipe given the fire rope and fire cement/HT silicon packing. I need to offset the flue by about 12" so I'll be using two 15 degree joints with a 1 metre straight pipe taking me up to the roof. I then assumed that I'd need a 5" chimney collar to take a short length of 5" pipe out to the roof and top it all off with a double skin chimney. But then I visited a chandler (who had no chimney collars) just to price up the collar - the information I was getting was that a 5" collar is for a 4" pipe and a 6" collar is for a 5" pipe - I left confused as I struggled to see that a 1/2" radial clearance was needed and that would take quite some packing.

 

Would some kind soul please clarify the pipe/collar size regime for vitreous enamel pipe installations as I may have misunderstood what I was being told.

 

Thanks

 

Martin 

[BEngo]

Most boat flues are fabricated from 113mm OD steel tube. That fits nicely into the standard squirrel collar, with room for some fire rope and a dollop of plumba flue sealant.  At the top, depending on the chimley collar,  it may be necessary to add a circle of 6mm bar on the outside of the pipe to nearly fill the space and support some more fire rope and another dollop of plumba flue to seal it.

N

 

PS Some confusion may arise from what exactly the pipe measurements are of.  Much imperial  pipe is measured by the Inside Diameter.  So a 5 in ID pipe would fit nicely in a 6in ID collar, because much of the gap is filled with the pipe wall thickness.

 

N

 

[dor]

Sounds about right.   My "4inch" flues is fitted to a 5inch collar.  Leaves room to pack in some FP rope, followed by a decent infill of high temp. silicone.

[Ex Brummie]

You needto pass your flue pipe through the collar, and ensure you avoid any metal to metal contact. Pack out with ceramic rope and HT silicon, and this will allow the fire and flue to expand and move through the collar. If you have a tight fit, then flue expansion will eventually split the top of your stove and/or buckle the side joints.

[Martin_B]

many thanks for you comments

[bizzard]

29 minutes ago, Martin_B said:

many thanks for you comments

I take it your using the lightweight sectional vitreous enamel flue pipe? which is good, far less weight pressing on the stoves top plate which is very thin cast iron on those stoves and can warp and crack them.