Originally Posted by CallMeVilla
Advice on the best orientation?
"Depending on the orientation that is right for your home, your tankless water heater can either vent horizontally through an exterior wall or vertically through your roof. It is very important you realize that you will not be able to use your existing venting with your new tankless system. You will need to use venting approved by the manufacturer.
You also want someone who knows all of the national and local codes that apply."
So I guess you should post a link to the make/model that you are using, and code excerpts. Each of us may get something different from this info.