What’s Included in a Standard Flue Extension Kit?
Each standard twin-wall pizza oven flue extension kit includes:
- Twin wall adapter
- 1 x 1000mm Twin Wall Length
- 1 x 500mm Twin Wall Length
- Rain cap
- Storm collar
- Fire cement
You can then select the flue lengths and parts to customise your flue system.
Before You Start
These kits are designed to connect to the original single skin flue supplied with your pizza oven.
If you’re planning to completely replace the original flue system, please contact us first, as flue sizing and compatibility may differ.
Why Twin Wall Flue?
Twin-wall insulated flue is designed to safely pass through roofs and structures while maintaining safe distances from combustible materials.
We do not recommend running standard single skin flue through a roof or enclosed structure.
Straight Up Is Usually Best
In most garden installations, running the flue straight up through the roof is the simplest, safest and most cost-effective option.
Trying to route “out then up” often creates unnecessary complications due to roof height, oven placement and support requirements.
Step 1 – Measure Your Existing Flue Diameter
Remove the rain cap from your existing pizza oven flue and measure the internal diameter of the pipe.
Common sizes include:
- 100mm
- 125mm
- 130mm
- 140mm
- 150mm
Getting this measurement right is important, as the twin wall adapter must match your existing flue size.
Step 2 – Work Out Your Required Height
Twin wall flue lengths are typically available in:
These can be combined to achieve the height needed for your installation.
Our Recommendation
Aim to have at least 500mm of flue extending above the roofline. This allows enough room for:
- Flashing
- Storm collar
- Rain cap
while also helping maintain proper airflow.
Do You Need an Offset?
If the flue outlet on the pizza oven doesn’t line up directly with the point where the flue needs to pass through the roof, you may require an offset.
Offsets allow you to adjust the flue route slightly without needing to reposition the oven itself.
A simple way to check:
- Use a plumb line from the roof exit point
- Measure the horizontal distance between this point and the centre of the oven flue outlet
If they don’t align, an offset section may be needed.
Step 3 – Choose the Correct Roof Flashing
The flashing type depends on your roof material.
Dektite Premium Black EPDM
Best suited to:
- Felt roofs
- Rubber roofs
- Metal roofs
- Timber garden structures
This style uses a flexible rubber boot secured using silicone sealant and self-tapping screws (not included).
Seldek Aluminium Black EPDM
Best suited to:
This is a more traditional aluminium-backed flashing option.
Both flashing types are suitable for roof pitches between 0–45°.
Optional Roof Support
A roof support bracket can be fitted beneath the roof between joists to help stabilise the flue system and reduce movement.
This is particularly useful on taller installations.
Step 4 – Prepare the Roof Opening
Recommended roof opening sizes:
Flue Diameter/Recommended Hole Size
100mm, 125mm, 130mm / 330mm
140mm, 150mm / 350mm
Always double-check clearances before cutting.
Step 5 – Installing the Flue System
Basic Installation Process
- Install the roof support (if being used)
- Insert the twin wall adapter into the original single skin flue
- Use the supplied fire cement if required for a snug fit
- Connect the twin wall sections together
- Secure joints using the supplied locking bands
- Lower the flue sections down through the roof into the adapter connection
Step 6 – Install the Flashing
Cut the flashing opening carefully to suit your flue size.
Recommended flashing hole sizes:
Flue Diameter Flashing / Hole Size
100mm, 125mm, 130mm / 190mm
140mm, 150mm / 210mm
Top Tip
Use sharp scissors rather than a Stanley knife for a cleaner cut on EPDM flashings.
Once cut:
- Position the flashing around the flue
- Secure it to the roof surface
- Seal as required
Step 7 – Final Assembly
- Slide the storm collar down the flue until it sits above the flashing
- Apply a bead of silicone sealant around the collar
- Fit the rain cap and secure using the locking band
Installation Complete
Your pizza oven flue system should now be safely extended through your garden structure and ready for use.
Correct flue installation helps:
- Improve safety
- Protect surrounding materials
- Maintain airflow and stove performance
- Reduce smoke issues around covered seating areas
If you’re unsure about sizing, offsets or compatibility, feel free to contact our team before ordering — it’s much easier to plan it correctly first time than modify it later
