Gas fire , chimney liner query. Minimum 125mm/5” ?

[Toby emery]

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

 

[ShaunCorbs]

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

Also any prevision for ventilation

 

[Aire]

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.

 

[townfanjon]

A gas safe builder , is it April 1st ?

 

[Riley]

Was gonna say be very wary and check no gas Safe person will mind showing their card.

 

[Toby emery]

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.

 

[ShaunCorbs]

Phone the manufacturer up they may have spec it

 

[Riley]

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

 

[sammathias]

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.

 

[Sharp Point]

I maybe going bonkers( I am getting old) but doesn’t an DFE ( basket)require 100cm of free air?

 

[sammathias]

I maybe going bonkers( I am getting old) but doesn’t an DFE ( basket)require 100cm of free air?

Noooo I would say a vast majority don't need additional air but some do. I don't tend to fit many mind so could.be wrong

 

[Aire]

I maybe going bonkers( I am getting old) but doesn’t an DFE ( basket)require 100cm of free air?

Yeah I was under the impression a dfe requires 100cm air vent, regardless of advinticious air.

 

[Toby emery]

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.

 

[Scott_D]

Hasn’t this type of flue and chimney added lots of cost to the job?

 

[Toby emery]

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.

 

[ShaunCorbs]

the manufacture will list something in regards to flueing

 

[Riley]

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

 

[Scott_D]

Get some evidence that you are not involved in fitting the gas fires

 

[Riley]

Good point Yes if you are doing gas runs and the wotsit hits the fan you need to distance yourself

 

[Sharp Point]

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.

 

[Riley]

It’s kind of all of the above mate. I’d be very sceptical of a bespoke fire full stop

 

[Toby emery]

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.

 

[Riley]

I’d steer clear unless you’re going to push your mate to find out more info

 

[firemant]

A BASKET fire requires 100cm of ventilation and a min 175mm flue.

 

[firemant]

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.