The HVAC metal ducting that goes into the attic for the cold air returns has two large holes in it with vents, right beside the gas water heater. If I remove the grills and cover up these so they can't get air, the duct work at that location gets sucked in slightly due to the negative air pressure (I think I'm saying this right.)
I read in a Popular Mechanics that you don't want cold air returns near the furnace. I know nothing about this stuff. Are these vents cold air returns? Is this an issue? Should I have these vents closed off and another cold air return piped to the hallway?