Double skin flue

[Dirk Pitt]

Hi one and all,

I have a query about the double skin flu of our log burner. No idea what make it is but it is a multi fuel, it also can heat hot water for the central heating.  The flue leaves the log burner and goes vertical for about a foot, then off at "45 degrees" for about 5 foot and then vertical.  It passes thru the ceiling, up thru the bathroom, thru the bathroom ceiling into the loft and out via the roof.

 

From the second "45 degree" bend the flu is double skinned thru the bathroom, no idea about the loft.

The double skin seems to be some form of plastic.  I would like to remove the second skin in the bathroom so the heat from the flu heats the bathroom.

Can I legally do this? What is the purpose of the second skin, I presume not to stop someone touching the flu as the log burner is just at hot. Is it due to the close proximity of combustible material?

If due to combustible material can I put a heat shield up and what is the distance the flue must be from combustible material if not double skinned?

 

I did contact Hetas and ask but they were unable to help

 

thank you in advance

 

Dirk Pitt

Edited November 30, 2021 by Dirk Pitt

[openspaceman]

2 hours ago, Dirk Pitt said:

The double skin seems to be some form of plastic.  I would like to remove the second skin in the bathroom so the heat from the flu heats the bathroom.

 

Not a good idea on two counts in my opinion. @Alycidon knows the rules, I am no expert.

 

1 The expose flue may burn someone and if combustible material (towels etc) may get too near they will catch fire

 

2 The exposed flue section would cool down flue gases at that point and could make tar deposits settle in the flue.

[Dirk Pitt]

1 hour ago, openspaceman said:

Not a good idea on two counts in my opinion. @Alycidon knows the rules, I am no expert.

 

1 The expose flue may burn someone and if combustible material (towels etc) may get too near they will catch fire

 

2 The exposed flue section would cool down flue gases at that point and could make tar deposits settle in the flue.

Thanks Openspaceman for the reply. The log burner could burn someone but that is not protected. I take your point about tar but what about those flu's that just go vertical up the chimney, if they are not double skinned would they too suffer from tar deposits ?  Point taken about towels, not something I had considered. thank you for making it

 

dirk pitt

[topchippyles]

10 minutes ago, Dirk Pitt said:

Thanks Openspaceman for the reply. The log burner could burn someone but that is not protected. I take your point about tar but what about those flu's that just go vertical up the chimney, if they are not double skinned would they too suffer from tar deposits ?  Point taken about towels, not something I had considered. thank you for making it

 

dirk pitt

Its double skinned for a reason so please do not go playing about with it. Common sense should tell you that.

[Dirk Pitt]

1 hour ago, topchippyles said:

Its double skinned for a reason so please do not go playing about with it. Common sense should tell you that.

I know it is for a reason but what is the reason? If to keep away from combustible material then asking if I can put a heat shield up shows I'm considering the safety aspect. If it is to stop people burning themselves then that train of thought is let down by the fact the log burner gets hot. If it is due to cooling and tar then removing it is a non starter but if flues that run directly up a chimney are not double skinned, then tar seems odd . Without me knowing the reason I cannot make an informed decision.  You have said it is for a reason but not told me what the reason is. Can you tell me what the reason is please?

 

Dirk Pitt

[topchippyles]

Few different reasons it would effect how the wood burner operates.You would have a cold spot in the chimney liner and that would effect the gases it gives off. 

[Macpherson]

28 minutes ago, Dirk Pitt said:

but if flues that run directly up a chimney are not double skinned,

I'd say these days they are or the flue is backfilled with insulating material like vermiculite for instance.

 

6 hours ago, Dirk Pitt said:

The double skin seems to be some form of plastic. 

Doesn't seem right.. but I'm no expert  on my stove the outer skin is often too hot to touch and in fact requires 2" clearance  in passing through floors  or roof, I think your best bet would be get your flue inspected by a professional to make sure it's safe 👍

[Commando]

As Mac says, if in any doubt get it inspected. I’d not even light it until I’d had a qualified and registered trade look at it. CO kills! And poorly installed flues can lead to house fires. It’s not worth the risk of messing about with.
Final point, if it’s not been inspected and it caused a house fire your insurance may not pay out.

[Dirk Pitt]

It had building regs when we moved in and since we moved in only a few months ago we have had it inspected and swept. We were concerned but the chap said all was fine.

We are having a second log burner installed but in a different roof in 3 weeks, I will ask the engineer to look the existing flue and give us advice.

 

thanks for the replies

 

Dirk Pitt

[Steven P]

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,.