Pipe Size


Dear NH,
I wonder if you have a recommendation about installing copper pipe. I am redoing my entire house from the main, and wonder if there is any advantage in using 3/4" copper pipe over 1/2" copper pipe. I am unsure, since the fixtures are all made for 1/2" pipe or smaller.

Dear RB,
There is no advantage to using 3/4" copper pipe only if the fixture is designed for 1/2"" or smaller pipe and it is the ONLY fixture on the plumbing run. In reality most plumbing systems run a number of fixtures from each main feed line. For example, a bathroom sink faucet, toilet and shower will normally share the same feed. In that case, I would suggest using 3/4" pipe and then reduce it to 1/2" where ever you need to connect a fixture. The logic is elementary. Drawing on my dim knowledge of geometry, the volume of water in any length of 3/4" pipe is more than double the volume in the same length in 1/2" pipe. By using 3/4" pipe, you can run multiple fixtures with virtually no drop in water volume .

If you have ever lived in a house where a nice hot shower turns scalding because someone flushed a toilet, or where your sink faucet drops to a trickle because the dishwasher turned on, you will appreciate using the larger pipe! Of course, if you have a well system with low volume output, the larger pipe will have less of an effect. It will help somewhat, though. You must also be careful with your hot water system. Some water heaters, especially "on demand" types (as opposed to tank water heaters) cannot produce enough water volume through a 3/4" pipe to supply fully heated water to multiple fixtures. Consult with the furnace documentation of a knowledgeable HVAC person for more info.

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