So I am new to this scene and am trying to install a Summer's Heat 50-SHW35 add-on furnace. I am installing in basement near my furnace. Floor is concrete and walls are preformed poured walls. My problem is that where I have to install the add-on, it is very close (6" or less) to my hot water heater. If this is considered a non-combustible, do I need to be concerned with the clearance between the two? I can't seem to find the right answer to this issue anywhere I look. The reason I have to install there is because of where the chimney exits the basement. Not sure what to do. Any help would be appreciated.