Black Twin Wall Flue Kit – Through the Roof with Offset (1–2 Story House)

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")

Passage of a flue through the floor

The passage through a flammable floor can be done with:

- a Ventilated Firestop plate against the ceiling (in practice customers often take a round trim plate for the first ceiling); and 
- a Vented Floor support on the floor.

1. Put a length through a pre-prepared wood box in the floor and slide down the Vented Floor support plate.

2. Screw this Floor support plate to the box. Next, screw the support clamp directly to the jacket pipe of the length. 

3 Glue the Ventilated Fire Stop plate (or round trim plate) onto the ceiling 

Introduce an offset in your flue (see picture)

Determine how many mm the flue should move sidewards.
To create the offset we can work with elbows of 15°, 30° or 45°. A lower angle is better for the draw.

Wall brackets

Both elbows need to supported by a bracket. These brackets can be a roof support, a wall support or floor support.

 Attention: You need to check if the required offset comes with an upward length that fits under your roof. If it does not; you need to find a solution, most likely go for a smaller offset...

The offset needs to be supported by two brackets; so that it does not sag. If this is not done by a floor support and/ or a roof support, you need to take one ot two wall supports (or find another solution).

We need to calculate how many straight elements we need going upwards; knowing that we already added some length to the flue through the adapter and the offset.

Step 1 : calculate how high the flue should be on the roof

To determine the required height on the roof (G)  see " Complete information" below.

Step 2: Calculate the total height of the flue (stove to cowl)

Total height of the flue  = B+C+D+E+F+G.   (In case of a 1 storey house; D, E and/or F can be 0)

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

Step 3: Determine how much length is in your shopping cart already

In your cart is already:

- the length from the offset - Question 4

Step 4: Calculate the length that has to come from the straight pipes

Total height of the flue - what is in your cart allready.

Note: a bit higher is okay, but do not take a lower height.

Chimney Heights and Termination

A 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 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.

The choice of the flashing depends upon:

- What kind of material material is covering the roof, and

- The pitch of the roof (0° being a flat roof, 60° a sharp roof)

Automatically we ad a roof support and -when required- a storm collar.

A finishing plate can be used to cover the opening between the flue and the ceiling under the roof. 

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.