Eric in North TX wrote:
I'm planing an install of a Takagi T-KD20 in the first floor of a 2
story addition. I'm a little confused by their install instructions. Do
I need to go through the second story roof with the exhaust vent?
My first choice would be to make it as short as possible. There are no
first floor windows on that wall, & only 2 on the entire wall, both 15'
or more from the intended location, there is a gable vent ~ 20' above
the intended location.

Perhaps I should have mentioned that a Takagi T-KD20 is a direct vent
tankless ho****er heater.