As part of a new residential boiler installation, two 6-inch ducts venting to the outside will be installed, one near the ceiling and one near the floor. They won't be attached to the boiler itself, as it's not the type of unit that takes direct venting. Just vents open to the room, but very close to the boiler and hot water heater.
The gas boiler and adjacent gas hot water heater are against one wall of a large space that is to be inside the thermal envelope of the house, but I think that lots of cold air will be entering through the new vents.
I want to build a closet around the furnace and water heater, and my question is: Should I seal it off and insulate it as much as possible, since it has it own source of outside air, or do I need a louvered door for some reason?
I'm pretty sure that with this amount of outside venting the right thing to do is to seal off the furnace. (There will be doors to allow access for maintenance.)