What is the difference between nonmechanical and mechanical air supply?
I am investigating purchasing a tankless water heater. When deciding location, horizontal vent location appears to be a big issue.
The distance between the HVAC air supply inlet and the water heaters concentric, combustion air inlet differs between mechanical and nonmechanical systems.
My HVAC unit is in the basement. I have a duct (?fresh air?) going from outside to the return plenum before the filter. Would this be considered a nonmechanical air supply inlet?