How do you find out what size pipe you should run for certain distances?

Answer 1

The Plumbing code adopted by the jurisdiction in which the piping is placed will assign a "fixture unit" value to fixtures. For example, for waste and vent piping, a lavatory is usually one, a sink is usually two, a toilet usually between three and six, etc. A chart in the code book will tell how many "fixture units" can be installed on a particular size line. For example, a 2" line will usually carry 16 fixture units on a vertical pipe, 8 fixture units on a horizontal pipe, and will vent 24 fixture units. For a specific answer to your need you should consult a plumber working in your jurisdiction. And as far as "certain distances".....horizontal is self-limiting by grade, vertical is addressed by code, for example, 2" is limited to 85 feet vertical. Pressure pipe (water) is done much the same way....fixture unit values assigned to fixtures and then total fixture units allowed for each pipe size and pressure range.