For many years, we have recommended only one PT-A-903 power vent for any insert configuration. This has proven to be adequate for exhausting undesirable odors. Additional power vents can be installed if desired, but it is not necessary for most applications. If you choose to block off the upper mesh area of the rear insert doors with the optional PT-A-913 cover panel, then additional vents should be considered. Roof power vents are not an adequate solution for air conditioning.