Workshop stove flue system information

Before you fill in our workshop stove flue design application it is very important that you read through the following information. It is for your own safety.

Should you run your workshop stove flue pipe internally or externally?

Running the flue internally is always the best and nearly always the cheapest option.

Running your workshop flue externally should be avoided if possible.

Why?

The flue stays much warmer when run internally and therefore less tar deposits inside the flue. Tar deposits lead to chimney fires, especially in long runs of single skin flue pipe.
Hot flue gases 'want' to go straight up - any bends in the flue system will slow them down and thus reduce draw. Most workshop stove flue systems are quite short anyway so it is best not to have bends in the system as these will further impede the draw.
The bends can also make it difficult to sweep the flue system. Sweeping a flue system is very important especially if large portions of it are in single skin flue pipe.
Bends and tee pieces are expensive components.

Single skin flue pipe

The temptation is to use as much single skin flue pipe as possible because it is cheaper.

Single skin flue pipe gets very hot
This is an important consideration especially if you want to run the flue near or through wooden or combustible materials. You will need to effectively heat shield the flue pipe or make sure that no combustible materials come within three times the diameter of the flue. So that's a 375mm clearance for 125mm flue, 450mm for 150mm flue, etc. You have to think of the worst case scenario which is a chimney fire in the flue - in this case the temperature of the flue can get to 1000-1200 degrees. So when you design your flue system you need to design it so that it can get to 1000-1200 degrees and not burn your workshop down. Chimney fires are much more likely in uninsulated flues as I'll now explain.

You get a lot of tar deposit in single skin flue pipe
Single skin flue pipe gets so hot because it is uninsulated so all the heat escapes. A common thing that people say is "great I'll make use the heat" that's OK up to about 2000mm but after that the flue gases will be significantly cooled. When flue gases cool tar and other deposits build up inside the flue pipe. This is what causes chimney fires. It is best to try to keep the length of single skin flue down to 2000mm to minimise on tar deposits and therefore reduce the risk of chimney fire.

Insulated flue pipe can be run within 50mm of combustible materials so is much simpler to install through a wooden roof for example.

If you are going to use insulated flue anywhere then the most important place to use it is for the roof penentration and outside portion. This is because the outside portion of flue will get the coldest.

If you do have long runs of single skin flue pipe then sweep your flue often this will help remove the tar desposits that will build up.

Support components

For workshop flue installations our customers generally make up their own metal support components and brackets to hold the flue and take the weight of the flue. We can supply these off the shelf but that bumps the price up. Just remember that the weight of the flue should not be sat on the stove.