Cast iron piping is still used in most commercial buildings like hospitals, hotels, vehicle dealerships, banks, office buildings, schools, lube shops and countless other facilities. Even though ABS or PVC piping can be used for commercial buildings according to the Uniform Plumbing Code (UPC), oftentimes other local or state building codes may specify cast-iron pipe be used due to various reasons. Some codes limit plastic piping to no more than two story buildings. Some buildings may fall under local codes for health or safety and cast iron piping may be specified because it is not susceptible to burning like PVC or ABS piping, should a fire occur.
Cast iron piping is often used in many residential multi-story housing projects because it provides a much quieter flow of waste water than either ABS or PVC plastics. If you have ever been in a room on the first floor of a two story building where ABS or PVC was installed and someone flushes the upstairs toilet, you would know what we mean.
Although no-hub couplings were designed for cast iron they are also a very handy way to repair ABS or PVC. They can be especially helpful when the piping is in a hard to reach spot or the pipe is unable to be moved in either direction to allow the repair to be made with a solvent (glue-on) coupling. The pipe can be cut to remove the damaged area and a no-hub coupling can be installed along with the replacement piping.
ABS and PVC schedule 40 piping have a slightly larger overall outside diameter than cast iron pipe. There is not a significant difference when comparing the outside diameter of 1-1/2″ or 2″ cast iron to 1-1/2″ or 2″ ABS/PVC pipe. For these two smaller sizes you could use a no-hub coupling to connect ABS or PVC directly to cast iron piping without a problem. However, if you are using a no-hub coupling to connect 3″ or 4″ cast iron to ABS or PVC then you will notice a more defined difference between the outside diameters of the cast iron and the ABS or PVC pipe.
To make it easier to adapt ABS and PVC to cast iron, the ABS and PVC fitting manufacturers created the ABS and PVC No-Hub Adapter fitting. One side glues over ABS or PVC and the other side is the same size as no-hub cast iron pipe. Without the use of these special adapters, the inner gasket of a no-hub coupling will stretch too much and not provide the best seal possible. Note: ABS and PVC are not compatible to glue together so if you are using PVC then you will need a PVC No-Hub Adapter fitting, and if you are using ABS you will need an ABS No-Hub Adapter fitting.