Twin Wall Flue - External - black-offset

Many wood-burning stoves come with the choice of attaching the flue pipe to either a top or rear flue exit. From the stove, you can lead the chimney directly outside, run it upwards first and then outside, or take the chimney all the way through the house.

For the adaptor you have the following options:

Single to twin wall adaptor (also increasing adaptors)

This adaptor can be installed in two ways:

1. Direct connection – push the adaptor into the stove opening so it sits inside the spigot of your stove. From there, connect the twin wall flue pipe above.
2. Connection via stove pipe – install a length of single wall stove pipe first, then push the adaptor into the top of the stove pipe and continue upwards with twin wall flue pipe.

Single to twin wall continental adaptor

A continental twin wall adaptor creates an easy connection of twin wall flue pipe to any European model of stove.

This Continental Stove Adaptor is used if you have a European stove collar, as the sizes are slightly smaller than a standard 5" or 6" stove collar.

• 5" continental adaptor: outside of the adaptor is 115 mm; to twin wall 125 mm (5")
• 6" continental adaptor: outside of the adaptor is 135 mm; to twin wall 150 mm (6")

The distance can be calculated as:  distance = G + E + D

G = distance heart of stove outlet - to- wall
E = thickness wall
D = distance outside wall - to - flue  (usually 50mm, but can go up to 350mm in case you want to go along a overhanging roof, without using elbows)

If the distance is fixed (you can not move the stove forward or backward) you will need an adjustable length. Choose one of the answers with a telescopic pipe; that pipe is included in the kit.

Together with the T135 piece, we will add:
- the adapter,
- the 45 degree elbow
- the wall sleeve. The wall sleeve is meant  to slide through the wall and to be cut to length as required. Add mortar around outside of it or fireproof insulation.
- 2 finishing plates, to cover the opening between the flue and the wall; both inside and outside.

There are three ways to pass the edge of the roof:

1. Straight along the roof edge
Choose this when the flue stays clear of the gutter at its distance from the wall (50 to 750mm). No extra parts are added here: the base support and wall brackets come from the question about the distance to the wall.

2. Straight up through the roof
Possible when the overhang is more than 30cm. We add a roof support and a flashing for your roof pitch (0-25 or 25-45 degrees).

3. Around the roof edge with an offset (see drawing)
Work out how far the flue has to come forward, and keep at least 10mm from the gutter. Wall brackets normally keep the flue 50mm from the wall, so an offset of 80mm gives 130mm between wall and flue. For a good draw we use two 30° elbows. We add the two elbows, an extra long wall bracket and, when needed, a straight length. Fix both elbows with a wall bracket and place the top bracket just below the gutter.

We need this to calculate how many straight elements we need to add.

1 Determine what the total height (S) of the flue should be

Determine the required height of the flue on the roof (M)  see " Complete information" below.

Now we know the total required height of the Flue (S) = M + L - K

M = Height of flue on the roof
L = Height of the gutter
K = Height of the stove

2 Determine the height you have already in the shopping cart

Part of the height is coming from parts already in your shopping cart:

R = Height coming from the Diagonal section going outwards (take from question about the horizontal distance)
P = Height coming  from the Offset - if you did choose one (take from the question about the passage along the edge of the roof) No Offset means P = 0.

3 Calculate how much height has to come from straight elements

Height straight parts = S - P - R

Check: The total height (S) from stove to end cap should be at least 3.5 meter (building regulation recommends 4.5 meter). 

You do not need to have the exact height, a little bit more is also okay (and cheaper than taking an adjustable length).

Chimney Heights and Termination

Simple rules

Within 600mm from the ridge
The flue has to end minimum 600mm above the ridge.

More than 600mm from the ridge
The distance between the cowl of the flue and the adjacent roof/wall/structure should be higher than 2.3 mtr. 

For the height of the flue on the roof this means:

All the rules

The minimum chimney height recommended for minimum performance of wood burning and multi fuel appliances is 4.5 m from the top of the appliance to the top of the chimney. In practice you 3.5m is often enough.

The distance between the cowl of the flue and the adjacent roof/wall/structure should be higher than 2.3 mtr. 

Within 600mm from the ridge: Flue has to end minimum 600mm above the ridge.

The diagram below, taken from Document J (building regulations), shows the minimum flue discharge heights and positions for all wood burning and multi fuel applications.

In some cases, particularly when chimneys are towards the bottom of a sloping roof or at the eaves, it may be necessary to increase the chimney height above these minimum mandatory requirements. The reason for this is to clear pressure zones created by wind hitting the roof and nearby structures, like trees, which may interfere with the up draught required by the appliance or fire.

The maximum freestanding stack height above the roof for a traditional masonry chimney is 4.5 times the narrowest horizontal part of the chimney.
In the case of stainless steel system chimneys, the manufacturer’s installation instructions should be consulted; however in most cases it will be around 3 metres. This measurement is taken from the last point where the chimney stack passes the through or past the edge of the roof up to the chimney capping or termination. Tall chimneys may need bracing, always consult the manufacturer for advice. 

For buildings with flammable roofs such as felted, thatched, or shingle roofs the flue or chimney the regulations are different. The flue or chimney must terminate at a minimum1800mm above the combustible surface.

Measure two things:

1. The distance between the wall and the flue. Wall brackets normally keep the flue 50 to 150mm from the wall. The flue can stand further out, up to 750mm, for example to pass an overhanging roof or gutter without elbows.

2. The length of flue along the wall, from the tee to the top of the flue or the roof edge.

What we add:
- 50 to 150mm: a base support, plus one wall bracket per 3m.
- 150 to 250mm: a long adjustable base support, plus one 150-250mm wall bracket per 3m.
- 250 to 750mm: long adjustable brackets. These carry the flue and hold it to the wall; one extra bracket per 3m.

There are 2 types of cap to choose from:

Rain cap
Will keep vertical falling rain out of the flue. In case of side winds, rain will enter the flue. In case of a flue outside this is less of a problem, as it will not floote into the house. 

All weather Cowl
Keeps rain out of the flue. Also blocks downwinds from entering your flue. Downwinds come from higher objects in the vicinity (up to 10mtr), and without this Cowl they will blow the smoke back into your house.

You need to support the flue over the roof if the free end becomes higher than 1.5m.

We recommend to use a Roof Stabiliser Bracket, if the free end is between 1,5m and 3m.

The bracket comes with two telescopic legs that extend from 1m-2m in length. Also a band which secures around the flue and connects to the legs.