A Studor vent is simply a valve that allows air into drainpipes when suction is present. The vent closes when the suction disappears to prevent foul odors from coming back into the building. Often, when a bathtub, shower or washing machine is bubbling or gurgling, either a Studor vent needs to be installed or an existing vent is locked in the open position.
Use the Studor Maxi Vent on drainpipes from 3 to 4 inches.The vent is manufactured primarily for commercial buildings, and is the largest one made by Studor, with a correspondingly large venting capacity. It can be "stacked" to provide additional DFU (drainage fixture capacity, a drainage measurement set forth by the Uniform Plumbing Code).
Vent as much as 160 DFU with the Studor Mini Vent, the type most commonly used in the household. This type is also equipped with an anti-rodent feature that can reduce extermination costs over the life of the product, according to Studor's website. Use this type of vent on 1 1/2- to 2-inch piping.
Add a Studor Ultra Vent in more constricted spaces. At 20 DFU, this vent has a smaller drainage capacity than the other models, but 20 is actually plenty for any single bathroom, sink or washing machine.