Ambient air

My grow room is in a tightly closed closet. Air intake can only be achieved from an outside source. The winters here are very cold and could significantly lower the grow rooms temperature. On top of that, there is no where for the air to escape freely. I cannot cut any vents or holes. Any suggestions?

I know you said no holes but your kind of screwed. If your intake is small enough you wont create too much pressure. But you wont move much air in the summer. If you cut a hole but dont go all the way through to the other side, you can vent some air through the space between the walls. You will need a filter or scrubber for flower time but it works if you dont have mass insulation in the walls.

I was thinking about dropping the closet doors down a bit to create a slot at the top. It will have to do, it's my only real option. Thanks for the input.

What bout a in room ac unit