All about Flues please .....why would one choose one with a double skin?

(Hilary Jane Dunk) #1

Hello all,

Still researching the wood burning stove side of things....unlikely to get one fitted before xmas (although I'd like to) as part of the existing chimney has a dangerous lean and will have to be taken down to a lower level, with some sort of pipe added to extend it to the right getting devis for this right now...Sorry have wasted time trying to import pictures for this, but I'm a novice Windows 8.1 user and I haven't been able to master this yet

Then of course there is the question of what type of flue to go for.....James ....there's your chance to let us know about your latest installation...

(John Withall) #2

Hilary, it is a good idea to fill the void between the pipe and the flue with vermiculite which isn't too expensive. If it needs a lot you have like myself one of those large chimneys. I am going to take down the large chimney and rebuild it in the terracotta blocks for the job as it will allow me to change somethings indoors too. It's to get a quicker warm up and better flue temperature to expel particulates etc. if the gasses cool on a long run then soot and particulates cal fall back down and in some cases cause a blockage which could be dangerous.

Another way to line it is when a team install a liner but way of an inflatable sausage which keeps the flue shape and then around the outside of the flue they pump lightweight insulating mortar. this can also be handy to stabilise a dodgy chimney stack.

(Hilary Jane Dunk) #3


Thanks to you both for this info.

I will look at the Hetas site.....I was a bit concerned because I had come across a website that insisted that it is essential to fill the void between the skin of the flexible liner and the chimney stack with some kind of granular insulating material....?

I would need an awful lot, I think.....

(Robert Scotton) #4

Aha....and there was me thinking you meant the solid double skin variety. Sorry, my mistake. All "multifuel" flexible flue liners are double skin. You just need to check it is not just for gas appliances. The bottom pipe, usually called the stove pipe, which connects the stove to the flexible liner can be a single skin. In either stainless steel (shiny) or stove enamelled steel (matt or shiny).

This should answer most of your questions and then there is the Hetas website as well of course.

(John Withall) #5

From information gleaned from the HETAS website (UK) single skin flue pipe is ok for gas etc but not good for wood burners as it doesn't have a reputation for lasting very long.

The majority of flue pipe sold for wood burners is double skinned, the way it's made may not look to some like it is but it has two skins.

Then we have the more expensive twin walled insulated flue, known as class 1 in the UK. This is used where the flue needs to be kept warm and it passes outside of chimneys which can be either inside or outside buildings.

That's a pretty simplified explanation but hopefully it sheds some light.

(Robert Scotton) #6

As far as I'm aware Hilary, you only need a double skin where you penetrate a floor or go through the roof space. you might see one in a modern house where the Flue is exposed or indeed a workshop. If you have a masonry flue already there is no need or benefit from fitting an insulated flue. The one that Brico Depot sell at around 28 euros per metre is all you will need. Woodburners generally work more efficiently with a flue liner rather than without one. I think that is due to a better "draw"......Shame you won't have it in before Christmas....good luck!!