There is no general rule, it depends on the type of environment which we are providing the air system for. For Office spaces, to meet comfort level, you need to provide the same amount of exhaust air for makeup air to balance the system (air balance) so to avoid space over-pressurization or negative pressure. Operation rooms in hospital or clean rooms should be in positive pressure to block entering viruses or dusts, while restrooms need to be in negative pressure to avoid odors from traveling to the adjacent spaces.
