CHIMNEY STACK DOESN'T HAVE A POT/COWL FOR BURNT GAS EMISSION

[LesWiggy]

I have lived at the same address for over 20 years & I had intended to replace my inset gas fire with a newer High Efficiency model. This would be the 3rd new gas fire in my time here. However the Gas Safe guy says I need a chimney pot for emissions. Currently the chimney stack has a concrete slab on top but there are gaps (house brick size) on the four sides of the stack immediately below the slab. I have had absolutely no problem in the past & the burnt gas emissions is evacuating through the ready made gaps into the sky. Surely this is perfectly acceptable. I can't find any advice which states I must have a chimney pot to evacuate the burnt gas emissions.?

 

[Blagard]

I think he has done the right thing as a slab over the chimney even with the holes you mention is a modification to the original flue and is incompatible with the way flues are terminated these days.

He is just following the requirements of the building regulations and unfortunately it is not always possible to replace like with like because of the such changes.

At the end of the day the Gas Safe engineer has to put his name to it that it is safe.

 

[Gas2Air]

I have lived at the same address for over 20 years & I had intended to replace my inset gas fire with a newer High Efficiency model. This would be the 3rd new gas fire in my time here. However the Gas Safe guy says I need a chimney pot for emissions. Currently the chimney stack has a concrete slab on top but there are gaps (house brick size) on the four sides of the stack immediately below the slab. I have had absolutely no problem in the past & the burnt gas emissions is evacuating through the ready made gaps into the sky. Surely this is perfectly acceptable. I can't find any advice which states I must have a chimney pot to evacuate the burnt gas emissions.?

What higher efficiency model was you hoping for?

 

[Steelmasons]

Nothing wrong with the way the chimney terminates.

 

[Gas2Air]

Nothing wrong with the way the chimney terminates.

Apparently the OP knows this.

 

[Steelmasons]

I think he has done the right thing as a slab over the chimney even with the holes you mention is a modification to the original flue and is incompatible with the way flues are terminated these days.

Absolute tosh , as long as ventilation is correct at opposite sides of chimney stack then not a problem.
For ventilation sizes then hit Google.

At the end of the day the Gas Safe engineer has to put his name to it that it is safne.

If he is worth his salts then why wouldn't he?

 

[Blagard]

I never had any doubt about the size of ventilation at the top of the flue given the information the OP posted. It was the manner of the work which is typical of what I would expect to see on a capped and ventilated flue.

If you guys know it is acceptable to the regulations then I'll bow to your knowledge.

So you advise the OP to get a different engineer in to do the work?

 

[Steelmasons]

If you guys know it is acceptable to the regulations then I'll bow to your knowledge.

Take a bow Blagard.

 

[Gasguru]

AFAIR provided the brick gaps are at least twice the cross sectional area of the flue and on at least two opposite sides then it complies. This is assuming the flue is at least 170mm across, if less then there are further regs. on the terminal construction.

 

[Steelmasons]

Chimney slabbed over , vents on both sides @ 120 cm² total free area.

 

[Blagard]

If you guys know it is acceptable to the regulations then I'll bow to your knowledge.

Take a bow Blagard.

I'm coming around but not 100% convinced yet and as GasGuru has flagged adds to the learning. If the flue is traditionally constructed it would be around 9" x 9" and each gap the OP posted about 9 1/2" x 3 1/2" max. I believe he has four about that. sorry for the imperial! That's a lot of vent but not twice the cross sectional area.

Is there a requirement for the flue to prevent rain, birds and leaves etc. from entering the flue ? That info is from online and not an official source so could be nothing but it makes me wonder so I may as well ask in the process!

 

[Steelmasons]

Chimney is slabbed over with vent grills (terracotta) positioned on the side of chimney stack , vent grills must be fitted as opposed to brickwork left out..
Minimum cross sectional area for OP gas fire is 12000mm² , so a minimum vent free area of 12000 mm² , or consult MI's.

 

[Blagard]

A lot of useful information there guys, but I am little confused about that flue cross section and how that figures in a domestic installation as it seems so onerous.

But more to the point it would seem the OP's Gas Safe Engineer had reason to be concerned. But quite possibly no "pot" would be required just a change to the way the gaps are created. Would even replacing a pot be acceptable?

I doubt genuine terracotta bricks will be up to spec unless the slab is raised. Is there an acceptable alternative like a metal louvre that would have a greater free area?

Any positive input for a solution for LesWiggy appreciated.

 

[Steelmasons]

Why the need to raise the slab?

 

[Blagard]

Why the need to raise the slab?

To get a 6" high terracotta in. The single course variety have a pretty low free area and ones I was looking up would not do it. You can get plastic ones that are terracotta coloured with much larger free area, but it seems reasonable to me that you meant real terracotta.