Discuss Viessmann external flue run conundrum in the Gas Engineers Forum area at Plumbers Forums

mutley racers

Gas Engineer
Hi all. Hope you have all been keeping well.

A while back I decided I only wanted to fit one brand of boiler and decided on Viessmann due to space for servicing and changing parts if ever needing to. I am finding my decision rather hard due to the different clearances on flue runs and cupboards to other boilers. Now I want to replace a 16yr old ecotec pro with a flat roof terminal which is adjacent to a window. Vailliant require 600mm which the current one is. Viessmann require 1000mm. Now I would need to run a flue externally up past the window and above the roof with a different terminal. Viessmann have an external flue kit which is 3 fittings and costs over £200! Anyone fitted one and know what this kit does? Any way, it makes it extremely expensive.

Now looking around, Atag give you 600mm and Baxi give 300mm clearance. What's the crack?

Rant over
You sure about vaillant as last time I looked it was 1500mm to a window and 600mm to
the edge / builders opening eg side so face on eg flue to window 1500mm vaillant would be

Eg c on the flueing diagram
Just looked at baxi there 1000mm as well eg s on theres


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Hi Shaun.

That's weird as I have just been looking on the baxi flue solutions. Maybe they made a mistake...

Looks that way as terminal distance from a wall is 300mm a well so can’t be the same for window to wall etc
Yes, vailliant are 600mm to nearest corner of the openable window..

But is your flue face on to a window that measurement is only for when the flue is to the right or left of the window if face on its 1500
As in Z in this image here.

Quite annoying having to type a lot of characters to post.


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Providing the terminal is more than 300 away from the opening of a window eg bottom of the window / builders opening

Tbh I would still use c on that as read notes 1-2

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