Appreciate any advice you offer. We are remodeling a basement in our 10 year old home by adding a bedroom to an open space that includes a furnace and water heater on one end. The furnace is a HE gas Trane unit with intake and combustion air vented outside, that was added last year by the previous owners. The 80k BTU gas water heater has an electric blower on top, but I believe the combustion air comes from the room. This new downsized mechanical room is about 9' x 11.5' with a 9' ceiling. There was conditioned air delivered into the room before the remodel started, but that has now been sealed.
Today our contractor said he needed to add an air passage vent from one of the adjacent living spaces to the mechanical room. Do we really need to do this? Can adding a replacement conditioned air vent meet this need?