Boiler Bolt-On · Flue route
Horizontal to vertical flue
A boiler flue takes combustion products safely outdoors. If a suitable wall exit is unavailable for the chosen boiler position, a vertical route through the roof may be considered. We plan the route and terminal before quoting.
Two possible routes
Wall exit or roof exit?
Both diagrams show an illustrative route from the same boiler position. They are alternatives, not two flues installed together. The exact terminal position, components and permissible length are set by the chosen appliance and survey.
How we choose the right route
Check the boiler position
We look at external walls, neighbouring structures, openings and where combustion products can discharge safely.
Plan the roof route
If a vertical route is needed, we assess the roof, internal path, clearances and access for installation and future servicing.
Confirm components
We select the approved flue kit, extensions and bends for the specific boiler, then list the roof work and making good in the quote.
What is involved
- Planning a flue path from the chosen boiler to a suitable roof terminal.
- Installing manufacturer-approved vertical flue components, supports and terminal.
- Making and weatherproofing the roof penetration with the specified flashing.
- Testing the completed installation and recording commissioning checks.
What we check at survey
- Whether a compliant horizontal wall terminal remains possible.
- Roof type, structure, loft access and a feasible internal route.
- Terminal positions relative to openings, adjoining structures and boundaries.
- Manufacturer limits for total length and bends, plus condensate drainage and service access.
What affects the quote
- Roof height, pitch, covering and safe access arrangements.
- Flue length, number of bends and required approved components.
- Openings through ceilings or roof, flashing and weatherproofing.
- Any boxing, specialist roof work or making good specified after survey.
What your written quote includes
- The agreed flue route and named components for the selected boiler.
- Roof penetration, flashing, access provision and weathering included.
- The extent of any internal boxing and making good.
- Testing, commissioning and clear exclusions or separately quoted work.
Vertical flue questions
Why not simply use a longer horizontal flue?
The terminal still needs a suitable position, and the chosen boiler has limits on flue length and bends. We assess both routes rather than assume a longer wall route will work.
Can the flue go through any roof?
No. Roof covering, structure, access, terminal position and compatible flashing all matter. The site survey determines whether a roof route is practical.
Will the roof be watertight afterwards?
The specified roof penetration and weathering are part of the planned installation. The written quote should identify the roofing work and who carries it out.
Can my old flue be reused?
That depends on the selected boiler and the manufacturer’s approved flue system. We specify compatible components after survey rather than promise reuse.
Are extra bends included?
Only the bends and extensions shown in your written quote are included. We list any additional route work separately when the survey reveals it.
Ask us about a roof flue route
Tell us your postcode, boiler location and roof type if you know it. We will check feasible routes before putting the scope in writing.
Prefer the website form? Contact MPH Boilers and mention “Horizontal to vertical flue”.