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Old 04-15-2009, 12:15 AM   #1
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Switch from 1/2" to 3/4" main water line?


I'm wondering if I can switch from a 1/2" main water supply to a 3/4" water supply anytime? Let me explain, I have 3/4" main from the water meter but when this (old house) was built, the 3/4" switches to 1/2" under a cement patio. It currently runs 1/2" throughout. My wife and I are adding to a master bedroom suite with a new bathtub, two head shower, 2 sinks, and an additional toilet. From everything I've read, 3/4" increases the volume of water so additional fixtures can be accommodated. I want to switch back to a 3/4" copper pipe only a few feet from where it converts to 1/2" in the first place. So, it will go 3/4" from the meter (under the cement), 1/2" for about 10 feet, then switch back to 3/4" for a main through out the house. Does this sound like the best approach?

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Old 04-15-2009, 05:54 AM   #2
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Switch from 1/2" to 3/4" main water line?


If it still uses the 1/2" at any point then the flow rate of 1/2" is all you will ever get.

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Old 04-15-2009, 07:36 AM   #3
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Switch from 1/2" to 3/4" main water line?


Most states require a min. of 3/4 inch some require 1inch. depending on amount of fixtures. In your case since you have 3/4 from the meter it would be best to run it all the way into the house. I personally do not like to run more than 3 fixtures on a 1/2 line although some codes say you can run as much as seven.
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Old 04-15-2009, 08:42 AM   #4
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Switch from 1/2" to 3/4" main water line?


I agree that you need 3/4" main water supply, but you need the entire line to be 3/4" with no downsizing in it. I always run 3/4" for feeding 1/2" take-pffs to each fixture and the the shut-off valve reduces it to 3/8" at the fixture (except tub and showers).
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Old 04-15-2009, 09:53 AM   #5
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Switch from 1/2" to 3/4" main water line?


I agree all incoming water lines should be or 1 inch. However if you have a regulator in the system somewhere after the ” run of copper changing even the entire run to ” may not make a difference if you are reducing the incoming water pressure significantly.

If you have an expansion tank in the system you can get a pretty good indication if changing to ” would be beneficial or not. Just put a pressure gauge in the system and have a few helpers opened a couple of faucets at the same time. The pressure will initially drop and stabilize. If the pressure drops again after it stabilizes for a few seconds upsizing the entire run of 1/2" to 3/4" will help. If it stays stable after the initial drop it would probably not make a difference going to or even 2” for that matter.

You can pick up a cheap gauge that simply connects to a hose bibb in the plumbing department at HD or Lowes for about $10.00.

Rege

Last edited by RegeSullivan; 04-15-2009 at 10:00 AM.
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Old 04-16-2009, 08:35 AM   #6
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Switch from 1/2" to 3/4" main water line?


Thank you all for your expertise, I'll see what I can do about extending the 3/4" main from the meter. The big problem is that I can't get to where it switches from 3/4" to 1/2", it is under cement. I might have to re-route the main entirely. Thanks again, this is a terrific forum!
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Old 04-16-2009, 10:09 AM   #7
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Switch from 1/2" to 3/4" main water line?


I would suggest you re- route from under the concrete.. If it's been there a long time. If the pipe in the concrete & isn't protected....You may have problems with leaks in the future
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Old 04-16-2009, 07:30 PM   #8
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Switch from 1/2" to 3/4" main water line?


[QUOTE][Just put a pressure gauge in the system and have a few helpers opened a couple of faucets at the same time. The pressure will initially drop and stabilize. If the pressure drops again after it stabilizes for a few seconds upsizing the entire run of 1/2" to 3/4" will help. If it stays stable after the initial drop it would probably not make a difference going to or even 2 for that matter./QUOTE]

never heard that before. will have to try that. kinda makes sense. why bother if the pressure's the same. BUT let ma ask you this, you can have lets say 40 PSI from any size line but wouldnt you have more volume with a larger line?
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Old 04-16-2009, 07:38 PM   #9
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Switch from 1/2" to 3/4" main water line?


Yes, you will have more volume with larger line
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Old 04-17-2009, 05:21 AM   #10
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Switch from 1/2" to 3/4" main water line?


[quote=II Weeks;261079]
Quote:
[Just put a pressure gauge in the system and have a few helpers opened a couple of faucets at the same time. The pressure will initially drop and stabilize. If the pressure drops again after it stabilizes for a few seconds upsizing the entire run of 1/2" to 3/4" will help. If it stays stable after the initial drop it would probably not make a difference going to or even 2 for that matter./QUOTE]

never heard that before. will have to try that. kinda makes sense. why bother if the pressure's the same. BUT let ma ask you this, you can have lets say 40 PSI from any size line but wouldnt you have more volume with a larger line?
1/2" should give adequate flow rate for any given fixture, the problem arises when more than one fixture is being used at the same time.
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Old 04-17-2009, 07:12 AM   #11
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Switch from 1/2" to 3/4" main water line?


Higher pressure in the 1/2" line can have the same flow as a 3/4" pipe at a lower pressure. Municipal water is usually higher pressure than what is recommended for residential plumbing. That is why many (most) homes have regulators set somewhere around 40 PSI. In my home the water comes in at 130 PSI. Also, check your water meter. There is a good chance it is 1/2". It might look like 3/4" but if it is threaded and looks like 3/4" is is probably 1/2".

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