Another flue question.

[coppice cutter]

Previously I provided background heat for my small shop from an oil-filled electric radiator, but when I realised that was going to be a considerably more expensive option in future I decided to pay a visit to my local stove supplier and see what I could pick up to replace it.

 

Long story short, I got an ex-demo Burley Hollywell which had been returned from their other branch because they found it difficult to light (the reason for which became obvious at a later date) therefore the vermiculite boards weren't even blackened, for a very respectable 500 quid cash, and no VAT. It's been sitting all summer simply because there's always something else here that needs doing, but now installing it is what needs doing, or at least the first moves in that direction.

 

So, the first run of flue will be two 45 degree bends with a straight bit in the middle to take it from the shop part of the building, through an internal wall and out in to the main part of the building and from there it will be roughly 8 or 9 ft straight up and through the roof. For that straight run I have heavy sidewall 9in mild steel flue pipe laying about which I could use, it would also give off a bit of heat along it's length in to the space which it's running through, but, will it loose too much heat to allow the flue to draw properly?

 

If it didn't work, I could always put a flexible liner through it and fill around it with vermiculite, but if there was much likelihood of that happening I'd just put in a length of twin-wall flue pipe from the get go and be done.

 

Thoughts?

[sandspider]

Do you live in a windy area? We live in a calm, still, cold valley, and lighting the woodburners is a bit of an art form due to the downdraught. Used to live on the side of a windy hill, and the draw through the flue was tremendous.

[coppice cutter]

Maybe not "windy" as such, but surrounding area would be flatish and to the south and west is a huge natural floodplain so there's certainly no adverse conditions to allow for.

[sandspider]

I'd have thought if you've got reasonable wind your draw would be ok on the flue you describe. But I am in no way an expert, so maybe don't listen to me!

 

Also, building regs may have something to say about single walled flue where people can touch it?

[Peasgood]

Try to have as much of the pipe immediately out of the stove straight up as you can before any bends, this affects the draw.

I would put insulated in from the start, if you have cold thick metal it will take ages to warm up and it will be tarring up in that time plus I don't think it best to go to 9" flue if you are trying to get it to draw. Plenty of log burners straight from the register plate to a brick chimney so it does work but not the better way to do it.

[Steven P]

'through an internal wall' - what is this made from? You'll need to take into account whether the flue could ignite the internal wall, any ceiling or surrounding materials (look above any ceiling too).

 

I think that 2x 45 degree bends are OK, can't remember if there is a minimum separation between them and also a minimum from the top of the stove, partly so that the sweep brushes and rods can navigate through.

 

Draw - depends a lot on the overall height of the system, 8 or 9' out of the shop part of the building, if you can get a 6' section on top of the stove as well then my mind says this is about the height of a bungalow - and stoves get installed OK and work OK in them. A lot of this depends on temperature difference (you get a better draw the day after a fire than when there wasn't a fire)., hot air rises

[Woodworks]

Dads got the same stove on a long uninsulated flue. Its a pain to start but great once up and running. Imagine you would have similar results with a large steel flue that cools quickly

[neiln]

I thought building regs only allow a short length, possibly 300mm but can't remember, before going to an insulated flue. The stove instructions will say what flue diameter you want, if it's a 5kW (or less) regs allow 5", iirc over 5kW needs bigger but the stove instructions over rule the regs. Smaller draws better, costs slightly less and is easier to install.

[coppice cutter]

On 20/09/2022 at 20:39, Woodworks said:

Dads got the same stove on a long uninsulated flue. Its a pain to start but great once up and running. Imagine you would have similar results with a large steel flue that cools quickly

Yeah, I'm hoping the fact that the uninsulated part is indoors will save the day.

 

If it was going through an external wall and upwards I'd definitely go insulated but if it works the heat from the steel flue will be useful background heat in the other part of the building as well.

[slim reaper]

If you intend complying with building regs then your not allowed to use flexible flue in anything other than lining an existing masonry chimney.