actually no...intakes and exhaust can and are completely sealed, just like the walk in door is sealed when closed. Dampers are put in place and controlled by other systems in the room. A controller is put in place to act kind of like a traffic cop, when the room is too hot it circulates fresh air into the room and exhausts the warm stale air. Once it reaches a certain pre-determined temps the vents close and at the same time your co2 injects fresh co2 into the room to be used up by the plants. You can control everything this way from temps to humidity...all automated. These controllers will create the perfect environment that you the grower set up this is a true sealed room which most of us will never achieve, anything less isn't really sealed, people just have different opinions on what is sealed and what isn't. There are tests to actually see how sealed your room is, do a little research and you can test your own room. Co2 can and does increase metabolic rates but everything else speeds up also, including diseases and other issues. Sealed or not...i don't recommend co2 to anyone until they understand the plants processes and usually by then they are more than happy with the system they have. jas