My house has an unused cistern that abuts the foundation. I've cut a doorway into it from my basement and would like to use it as living space. I would like to install a door to obscure and soundproof the room, but that would cut off the only source of air to this air-tight space.
I can install a vent by drilling through the basement wall at another location, but I am wondering how can I safely ventilate the 600 ft³ room so that several people can sit in it for hours at a time.
I would prefer a smaller hole, which will I imagine will require an fan as opposed to just a hole. Does this mean I would also need a second hole to return air, or could enough air escape around the door?