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 most likely need to use a adjustable flue pipe. You can add this later to your basket.

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 3 ways to pass along the edge of the roof:

1 Straight upwards through the roof

This is possible when the overhang is more than 30 cm.

We add a wall support bracket, a flashing, and a roof support to the shopping cart.

2 Straight upwards along the edge 

We add a wall support bracket to your shopping cart.

3 Around the roof with an offset (refer to the drawing).

Calculate the necessary forward extension for the flue (maintain a minimum distance of 10mm from the gutter).

Typically, the wall brackets employed along the wall provide a 50mm gap between the wall and the flue. Therefore, an offset of, for instance, 79mm results in a total distance of 129cm between the wall and the flue. For optimal draft efficiency, it's advisable to utilize two 30º bends. Both bends should be secured using wall brackets. Ideally, position the upper wall bracket just below the gutter.

During this stage, we will add 2 x 30° elbows, an extended wall support bracket, and, if necessary, a straight component.

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 mtr. 

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.

You need a base support unit to that carries the weight of the outside flue. (A wall support only gives sidewards stability)

You can choose between:

- Base Support Bracket : Can carry the weight of maximum 5 m of flue

- Base Support: Can carry the weight of up to 12m of flue

Type of Wall support 

Normally the wall supports with a 50 - 70mm distance wall - flue are taken.

With the offset, we already added an extra-long wall support for the upper 30° elbow. Here we add another 50 - 70mm wall support for the lower 30° Elbow.

Number of Wall supports

This depends on how many meters the flue goes along the wall.
We recommend to use a wall support  every 3 meter along the wall.  So every 2 - 3 meter above the T135 piece; 1 wall support.

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.