Im building a bit of a lab at home, for bacterial work. As stupid as this sounds, im a bit confused about setting up air filtration. So the lab will be lined with plastic sheets, air tight. i intend to set up a HEPA filter, to filter incominng air. But thats going to make it a pozitive preassure room. Should i set up a place for the air to leave? is just a filter and a fan enough for the out going air?