I inspected a room with 100,000 BTU natural gas furnace and 36,000 BTU hot water tank in a 6X6X8 room. No exterior ventilation for combustion air. Door to room was trimmed at bottom allowing house air to enter for combustion air. I am going to recommend an exterior vent added for combustion air. My question is: There is currently an exterior vent with ducting into the return air plenum. Should I recommend the return air plenum be sealed from exterior vent and exterior vent be allowed to add air into small utility room for combustion air? Thank you.