Double skin flue

[Dirk Pitt]

4 minutes ago, Steven P said:

I have a single skinned flu up the chimney, and where it passes though the bedroom that part of the chimney gets nice and warm to touch. A double skinned flu I guess will get equally warm, and i wold be tempted to leave it as it is.

 

You can use a stove with a single skin, like mine up a chimney or a double skin like yours (or also up a chimney), this extra insulation stops the gasses cooling too much and the tar sticking to the flu, chimney needs to be swept less often (though still at least once or twice a year) and a hotter exhaust at the top improves the draw at the bottom,.

Thank you

 

Dirk Pitt

[Alycidon]

Sorry for the late reply, simply swamped with demand for stoves and would at present.

The installation of a stove is a notifiable event, this means your local building control office needs to be informed.    It also needs to be installed as per the instructions in the front end of Approved Document J of the building regs.   If its not signed off or not installed to the regs if you ever have a fire your insurers will invalidate your cover and not pay your claim.

 

So let's look at whsts needed,  single skin pipes and flexible flue liner can only be used inside a brick or masonry chimney.    A flue system like yours is fully insulated,  while you can use up to 1.5m of single skin off the top of the appliance everything above that has to be twin wall.  This is legal requirement,   bear in mind that the minimum combustible clearance on a single skin 150mm pipe is 450mm.   Roof rafters,  ceiling joints, plaster board on the ceiling are all highly combustible.

 

In upstairs rooms and lofts the twin wall pipes are required to be boxed in,  again  safety measure to protect against fire.  Yours is not boxed in and you are asking about removing the insulation material.   This is as large a NO WAY as I can give you.   The insulation is there to stop the pipe setting fire to your property and the outer skin of it are structural and likely to be holding up the pipes above it.

 

One final issue,  I have never seen a twin wall solid fuel flue that is anything other than stainless steel or zinc coated in construction.   That yours has a plastic or similar cover suggests to me thst the flue you have is not a solid fuel one.  

 

My best advice to you is to get a professional independent installer in to check the install but if its as you say it will be condemned as unsafe.  That Hetas were not prepared to comment does not surprise me,  your description raises huge red flags and you should have at least been told to get a registered installer in to check things out, that's why I resigned some years ago and joined the SIA.  

 

Please do not cut thst insulation material away.

 

A

 

 

 

[Dirk Pitt]

1 hour ago, Alycidon said:

Sorry for the late reply, simply swamped with demand for stoves and would at present.

The installation of a stove is a notifiable event, this means your local building control office needs to be informed.    It also needs to be installed as per the instructions in the front end of Approved Document J of the building regs.   If its not signed off or not installed to the regs if you ever have a fire your insurers will invalidate your cover and not pay your claim.

 

So let's look at whsts needed,  single skin pipes and flexible flue liner can only be used inside a brick or masonry chimney.    A flue system like yours is fully insulated,  while you can use up to 1.5m of single skin off the top of the appliance everything above that has to be twin wall.  This is legal requirement,   bear in mind that the minimum combustible clearance on a single skin 150mm pipe is 450mm.   Roof rafters,  ceiling joints, plaster board on the ceiling are all highly combustible.

 

In upstairs rooms and lofts the twin wall pipes are required to be boxed in,  again  safety measure to protect against fire.  Yours is not boxed in and you are asking about removing the insulation material.   This is as large a NO WAY as I can give you.   The insulation is there to stop the pipe setting fire to your property and the outer skin of it are structural and likely to be holding up the pipes above it.

 

One final issue,  I have never seen a twin wall solid fuel flue that is anything other than stainless steel or zinc coated in construction.   That yours has a plastic or similar cover suggests to me thst the flue you have is not a solid fuel one.  

 

My best advice to you is to get a professional independent installer in to check the install but if its as you say it will be condemned as unsafe.  That Hetas were not prepared to comment does not surprise me,  your description raises huge red flags and you should have at least been told to get a registered installer in to check things out, that's why I resigned some years ago and joined the SIA.  

 

Please do not cut thst insulation material away.

 

A

 

 

 

A very full explanation of why not to remove the outer skin, thank you. It seems a shame to waste all that heat and the regulations seem short sighted if they have included other forms of protection against fire for example, double skin where it passes thru floors and ceilings, close to combustible material etc. You mention nothing about gasses cooling and tar, does that mean that what has been said in previous replies does not apply?  Seems the flue will have to stay but boxing in a twin skin flue to prevent fire seems unnecessary as the prevention of fire is the role of the second skin

 

Can you advise where I can get hold of a copy of the UK regulations that apply for the installation of a log burner and what the regulation is called?

We have building regs for the installation.

thank you in advance

 

Dirk Pitt 

[Stubby]

45 minutes ago, Dirk Pitt said:

A very full explanation of why not to remove the outer skin, thank you. It seems a shame to waste all that heat and the regulations seem short sighted if they have included other forms of protection against fire for example, double skin where it passes thru floors and ceilings, close to combustible material etc. You mention nothing about gasses cooling and tar, does that mean that what has been said in previous replies does not apply?  Seems the flue will have to stay but boxing in a twin skin flue to prevent fire seems unnecessary as the prevention of fire is the role of the second skin

 

Can you advise where I can get hold of a copy of the UK regulations that apply for the installation of a log burner and what the regulation is called?

We have building regs for the installation.

thank you in advance

 

Dirk Pitt 

The more you insulate a flue the less likely you are to have cooling gasas and condensation .

Edited December 7, 2021 by Stubby

[Dirk Pitt]

22 minutes ago, Stubby said:

The more you insulate a flue the less likely you are to have cooling gasas and condensation .

just like an exhaust on a car but if you run the engine for long enough the heat transfer will dry out the exhaust

would the same be for the flue, uninsulate it, but heat it for a long time and it will dry out and get hot?

 

dirk pitt

[openspaceman]

5 hours ago, Dirk Pitt said:

Can you advise where I can get hold of a copy of the UK regulations that apply for the installation of a log burner and what the regulation is called?

Approved Document J | Part J - Combustion appliances and fuel storage systems | Planning Portal

WWW.PLANNINGPORTAL.CO.UK

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Details of Part J (Approved Document J) of the Building Regulations

 

[Doug Tait]

Mentioned in the original post that the stove heats water for radiators. Maybe you could heat the bathroom that way instead. 

[Alycidon]

You can download Approved Document J from the govt website. Page 1 of Google is usually full of people trying to sell it to you , the site you want will probably be on page 2 where you can download it fir free.  You want the 2014 version ideally but the older version will do as it covers this aspect. 

 

When I read your post I did not see anything about tar,  but let's talk a bit about thst.

 

Creosote occurs naturally within pretty well all woods.  When loaded into a stove the creosote is given off in gas form and providing the temperature is hot enough to combust the gases. 

 

The problems come when A. wet wood is loaded,  thus all the energy is used to evaporate the remaining water in the log and there is not enough energy left to get the temperature in the firebox above the combustion point of the creosote gases. And B when a stove is run closed down fir extended periods.

 

If the temperature in the firebox drops below the combustion point of the creosote gases then instead of burning in the firebox they get up into the flue,  condense in the flue, and line the sides of the flue with tar.  

 

So removing the cladding in the bedroom would not have an effect on the tars forming as thst occurs in the firebox,  but in the event of a chimney fire caused by tar deposits things would get very dangerous pretty well immediately.   

 

A

Edited December 8, 2021 by Alycidon