I have a question on inside tankless water heaters and makeup (combustion) air that feeds them. I have had problems with plumbers saying it is o.k. to have the makeup air come from inside the home, and not be vented into the intake of the unit from outside (Mostly A.O. Smith brand). The installation directions say it can be installed both ways, but does not specify if it is in a Garage ( where more air is available through the garage doors, or inside a home). Especially with newer homes and these units drawing lots of inside air.
Opinions and facts please….