In some instances, exterior venting may not be an option. If you are looking for a relatively inexpensive yet quality brand central vacuum system power unit which does not need to be exhausted to the outside of the home, the Vacuflo Filtered Cyclonic models may be a good choice. Designed to fit into inner city row homes and townhomes, this line of power unit has one 7" or 10" cartridge filter that keeps the traps airborne dirt before it gets into the motor cavity of the unit. At least 90% of the dirt is sent to the dirt collection canister through cyclonic momentum, much like the True Cyclonic power units.