they are typically the size of a wall receptacle and have a cover over the port. i don't understand the complaint of "asthmatic" above - it doesn't make sense. there is no air circulating in the living area. as well, the only noise you'll have will be the suction and the agitator brush, not the motor (it will be minimal, if any).
pio - how complex/time consuming was the installation? Is it difficult to have done in an existing home?