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Discuss Gas fire , chimney liner query. Minimum 125mm/5” ? in the Plumbing Jobs | The Job-board area at PlumbersForums.net

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hello,

I have a question regarding the minimum size of a chimney for a gas fire.

The builder doing the house refurbishment has apparently got fires included in his gas safe, so they are undertaking the work.

They are building a chimney breast from new, there are 2 basket gas fires rated at 6kw each. They have built the builders opening and attached a chimney gather on top. This is where my question lies, they have used from the gather a twin lined flue system but with a diameter of around 350mm? One for each fire.

The client, my friend asked if this was overkill as the chimney breasts are not huge and take up a huge chunk of there 3 rooms in which the chimney breast is. I said I always thought the minimum was 125mm/5 “
The builder has said he’s asked many people for advice and is adamant that they are the correct size. What are your thoughts on this?

Thanks

Toby
 
What do the manufacturers instructions say and have you checked he’s gas safe ?

Also any prevision for ventilation
 
The manufacturers instructions of the fires you are installing will tell you all you need to know, and id also be wary of a builder who claims he's gas safe, 100% of the builders I know certainly aren't.
 
Was gonna say be very wary and check no gas Safe person will mind showing their card.
 
My thoughts exactly when the client told me they are doing the flues! As I said I can’t do the fires for you as I haven’t got that qualification.

No they are only 6kw so adventitious air will suffice. One in each room not in the same room.

They are hand made and all the manufacturer gave were the dimensions for the builders opening. If you were to put a flexible flue liner down a chimney and seal off the opening with a debris plate then I’d imagine you’d use a minimum of 5” diameter flue? You wouldn’t and couldn’t drop down a 13” twinwalled flue (inner diameter ) !

So just curious as to where he got this huge diameter from as he claims he’s asked many people. And my client is now asking me if he can get someone else in could they decrease the size of the flues.
 
Phone the manufacturer up they may have spec it
 
Something doesn’t add up here. All the gas fires I’ve fitted give you the ins and outs of a cats backside in the instructions. Also, because they are 6kw doesn’t mean AA is always sufficient
 
Yes a DFE fire does need free air as not a clean flame. I’m not getting too involved with it, well I guess I am, I am on a forum asking questions!

Manufacture asked him if he wants a fire which doesn’t require extra ventilation. The house is 200 odd years old and with floorboards as flooring. I wouldn’t trust AA in a new a build.

If the manufacturer doesn’t mention anything then you would go to what the regulations say ?

As said I haven’t got a qualification for fires so don’t know too much about them. The builders opening goes to a gather plate then on top of that is stainless steel tube going to outside through the roof. As said 13” seems overkill when the regulations I’ve read a gas fire must have a minimum diameter flue of 5”.

Even with a 5” flue they are like 20% efficient so with a 13” flue it’s going to be 0% with huge drafts. Like with water you can have too big of a pipe which will produce a linear flow, surely a flue should promote a turbulent flow.
 
Hasn’t this type of flue and chimney added lots of cost to the job?
 
image.jpg
Yes it has, as said it’s not on my costs. I’m only doing the heating and the gas feeds.

But the client isn’t happy as it is humongous and ugly, and he just asked if I could give advice on whether they need to be that big. One flue run is 5m with 2 45’s the other is maybe 3m straight run.

The builder is adamant and is not going to change them as they are now enclosed and decorated. But client is thinking of ripping it all out and start again and use smaller pipe. I personally would be happy using a 5” pipe as from what I’ve read. But I can’t do the work.
 
the manufacture will list something in regards to flueing
 
Contact the manufacturer. Their word is gospel. And seriously ask for the GS qualifications of the builder if he is willing to crack on without
 
Good point Yes if you are doing gas runs and the wotsit hits the fan you need to distance yourself
 
Also and I might be having another blonde moment, but doesn’t the height of the gather and size of the opening have to be a certain sizes. I haven’t done one in years, but I feel as if there’s requirements.
 
It’s kind of all of the above mate. I’d be very sceptical of a bespoke fire full stop
 
This is why I wouldn’t get my fires as I wouldn’t want to put my name to one! Thanks for the advice anyway. That’s the one dimension they did give, the builders opening. And it’s 1m straight from the gather plate to the first bend which it was.
 
Brand new chimney? Don't necessarily even need a liner. Manufacturer will say if it needs air vent...if it's s DfE then could potentially need air even if it's only 6kw.


If I have understood correctly, he is not buiding a chimney. He is using rigid twin wall flue.

350mm is way too big, it almost certainly should be 175mm, plus the the second skin, so around 225mm in total.
 
View attachment 37204 I personally would be happy using a 5” pipe as from what I’ve read. But I can’t do the work.

You would be wrong.

Is the chimney breast built in block/bricks, or timber?

Tell the owner to contact gas safe. The fires must be notified, and the flue comes under gas work. Use the GS find an installer to check his registration or ask GS.

A registered fire guys should not be asking "lots of people". Flue if that type and size is horrendously expensive (and it will be insulated) - it probably would have been cheaper to build a proper chimney. Assuming, of course, that it has been procured legitimately.

- Direct Flues

Furthermore, only a nutter these days would fit a basket fire. As has been pointed out, they are pretty much decorative only. With a correct ventilator, they can actually have a NEGATIVE efficiency. The 6Kw is never going to heat a decent sized room, so central heating will be on. The fire heats up the chimney, massively increasing the air changes in the room, which will suck out the warm air heated by the rads.

This will not end well.
 
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