I am finishing my basement and enclosing my furnace and tankless water heater in an unfinished utility room. Both the furnace and tankless water heater are direct-vent systems pulling air from the outside. Do I still have to put in the 2 vents (1 high and 1 low) in the walls for combustion air? It's a 60,000 BTU input furnace.
To my knowledge there is no code requirement that the room be vented with high efficiency direct vent appliances. As you said, both systems provide their own combustion air from outside the building envelope.
However, it's likely that a tightly enclosed room will get quite warm at times. You may want to provide a means for heat escape.