How to Size Plumbing Pipes

Getting the right plumbing pipes will determine the way the water flows from the main water inlet valve to the faucets. A supply pipe is only able to supply a certain amount of water at a certain pressure. If the plumber installs the small size pipes, the amount of water is restricted while larger pipes may produce too much flow for many fixtures.

• Check the local building codes to find out the details of the fixture units. This is the amount of water per cubic feet expelled every minute. This information will enable you to get the right size and type of pipe. The building code will help you to determine the pipes used in each situation.


• Measure the length of the distribution pipes that you need for the entire plumbing system. Find out the size of the main pipeline that connects the water into the house. A larger pipe will expel more water into the house than a small one.


• Consider the number of fixtures and appliances in the house and calculate the fixture unit ratings for each.


• Determine the hydrostatic head of the system. This is the vertical distance of the water line. When pushing water up like from the basement, there is a lot of gravity to contend with. Water pressure reduces with every foot that the pipe extends above the water supply.


• Reduce pipe noise by using large diameter pipes as well as using thicker walled pipes. If copper tubing is used, make sure it is thick enough. L copper will absorb more sound as compared to the commonly used M type copper.


• Inspect the areas where the pipes are going through. Wall plates and studs as well as floor joists have to be the correct size. They should not restrict the pipes. Slightly oversized wall plates or stud holes ensure that the pipes can expand and contract unhindered.