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Boiler: Viessmann Vitodens 100-W Questions

I'm replacing my boiler for a Viessmann Vitodens 100-W (Category IV). I'd like your help deciding whether to take fresh air from inside or outside my house.

If it gets air intake from the surrounding room instead of outside, would there be any concern of CO backdrafting into my house?

Does it become a Natural Draft (Category I) boiler if I use air from the surrounding room? Or is it Category IV regardless of configuration?


  • VictoriaEnergy
    VictoriaEnergy Member Posts: 126
    Outside air

    You should definitely have the comb air piped directly from outside.  There will be less dust and other contaminants present in outside air.  The inlet should be located away from dryer vents, pools or hot tubs too.  The added cost should be minimal, and its beneficial for the longevity of the boiler.
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