The RTA series upblast roof mount axial exhaust fans are the right choice for higher CFM's needed. Up to 75,000 CFM available. Roof exhaust is often used when space is limited for wall exhaust fans to be installed, or in conjunction with wall mounted fans. The upblast type roof fan is often used when the air being removed is clean and minus any chemical particulates. The downblast roof exhaust fan is for those applications where the air is not to be sent up into the atmosphere due to caustic or harmful particulates that may be present.