Confused about chimney

[Phil Ambrose]

I'm a bit confused by M.C,s' website. They sell 2 sizes of roof collars, 6" and 5" but chimneys come in sizes such as 4 3/4" , 5 1/8", 5 3/4" etc, etc. I understand that roof collars are tapered but why the big (1/2") difference surely one chimney at 5 1/8" dia would rattle around loose on a 5" collar while a 4 3/4"dia would be perhaps too tight to get on or at least to sit on properly. Anybody care to enlighten me?

 

Phil

[Guest wanted]

I'm a bit confused by M.C,s' website. They sell 2 sizes of roof collars, 6" and 5" but chimneys come in sizes such as 4 3/4" , 5 1/8", 5 3/4" etc, etc. I understand that roof collars are tapered but why the big (1/2") difference surely one chimney at 5 1/8" dia would rattle around loose on a 5" collar while a 4 3/4"dia would be perhaps too tight to get on or at least to sit on properly. Anybody care to enlighten me?

 

Phil

I wonder if they are measuring I/D and O/D? Also allowing for movement during heat change?

[davey b]

There is the inside diameter of the collar to consider, some of the collars will have different wall 'thicknesses' - and then there is the single/double skin question.

[PhilR]

I'm a bit confused by M.C,s' website. They sell 2 sizes of roof collars, 6" and 5" but chimneys come in sizes such as 4 3/4" , 5 1/8", 5 3/4" etc, etc. I understand that roof collars are tapered but why the big (1/2") difference surely one chimney at 5 1/8" dia would rattle around loose on a 5" collar while a 4 3/4"dia would be perhaps too tight to get on or at least to sit on properly. Anybody care to enlighten me?

 

Phil

 

MC? - do you mean Midland Chandlers?

[Keeping Up]

Perhaps to fit existing (and older) collars that were supplied by other chandlers?

 

What does annoy me is that their double-skinned chimneys no longer fit snugly inside their own collars, to the extent that they are useless unless you fill them with fireproof foam. I had to buy a single-skinned chimney and a separate liner, then pop-rivet them to fit. Hopefully however the upside is that if the liner outlives the outer it should be possible to transfer it to the next chimney.

[Phil Ambrose]

MC? - do you mean Midland Chandlers?

 

 

Er, yes, sorry I should have put in full name.

 

Phil