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Properly Size Your Water Lines

My guess is that most people don't think twice about the water that will flow from the faucets in their new homes. You may not even give a second thought to the noise water makes when rushing through water lines. Because you are moving into a new home, my guess is you might assume a waterfall of water will cascade from each faucet and hose bib. Don't count on it. Your builder or plumber may have made a few mistakes that can restrict the amount of water that flows from faucets. These same mistakes can also cause significant water pipe noise that drowns out conversation and other pleasant sounds around your home.

If you are in the planning stages of building, you can correct these problems before they happen. A water supply pipe of a given size can only supply a given quantity of water at a given pressure and a given hydrostatic head. Hydrostatic head commonly refers to the vertical distance a water line extends. If you are trying to push water up a pipe from a basement to a second floor, gravity is doing its best to exert an opposite force against the water pressure. Gravity becomes your friend and increases water pressure if you store your water up on your roof, but how many people do you know have 5,000 gallon storage tanks in their attics?

Plumbers and builders know that people rarely turn on more than three or four plumbing faucets at the same time. But it can happen. If you want a plentiful supply of water to flow from each faucet, you must be certain that the main water line entering the house and the main feed line within the house is three-quarter inch in diameter or possibly one inch in diameter. This larger sized pipe can carry a significant amount of water.

All too often, a rookie plumber might start to prematurely reduce the size of the water lines in a home. If you see one-half inch diameter water lines that serve two or more fixtures, trouble may be just around the corner. If your new home has three or more bathrooms, consider keeping the cold water pipe size one inch until it has served the water heater, the first bathroom group and possibly one or two outdoor hose bibs. The main water line can then be reduced to three-quarter inch diameter to serve the remaining bathrooms, laundry room, hose bibs, etc. One-half inch diameter pipes can branch off the three-quarter inch line to serve individual fixtures. Extend the three-quarter inch line until you get to the final two or three fixtures in the house.

Pipe noise is also a function of pipe size. Larger diameter pipes create less noise because the velocity of the water moving through the pipe towards the fixture is lower. You can also minimize pipe noise by specifying a thicker pipe size. If you are using copper tubing in your new home, it is very likely that type M copper will be used indoors. This is the thinnest pipe allowed by most plumbing codes. Thin pipes transmit noise more readily than thicker-walled pipes.

The next thicker pipe type is L copper. Look at a piece of L vs. M copper and you will not see any difference. But pick up a 10-foot long piece of each and you will immediately realize the type L copper weighs more. This extra copper absorbs sound. The fantastic news is that the cost upgrade for type L copper in a typical residential home is less than $75.00. This is a one-time fee that allows you to have quiet water supply piping for the life of the home. It is a very small price to pay for peace and quiet.

Finally, be sure the pipes are not in a bind as they pass through wall studs, wall plates and floor joists. The holes need to be slightly oversized so the water pipes can expand and contract freely. Pieces of rubber that absorb vibration can also be installed between the pipes and any wood framing. Installing the strips of rubber can be a hassle, but any acoustical engineer will tell you it helps to stop noise transmission.

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5 Responses to Properly Size Your Water Lines

  1. I have a new house and my water comes from a well. The builder
    had young plumber to do the plumbing but he plumb my riannis
    wrong so I just got done replacing the pipe. My question is
    the pipe from the well is two inch then he put a three inch piece of
    one inch to a shutof then ran three quater to half thru the house.
    I am in the process of fixing it. I would like to know if I should replace
    the pipe with one inch to half inch to my fixtures. Thank you
    Richard

  2. I'm replacing a water line supplying a three bedroom two full bath home. Distance from meter box to house is 400 feet, water diameter line do I need? PVC vs PEC?

    • You won't go wrong with an 1.5-inch diameter line. What plastic is approved by your water company?????? Do your research online for FAILED stories about either material in your area.

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