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Plumbing Question - Domestic Water Main Size

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Plumbing Question - Domestic Water Main Size

Old 08-31-2011, 02:08 PM
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Default Plumbing Question - Domestic Water Main Size

I know some of you folks can easily explain this to me...

Plumber just did calculations for a home's water service, says minimums are:

(1) 3/4-inch pipe for domestic water main (from city main into the house),

and then

(2) 1-1/4-inch pipe inside the house until enough "units" fall off, then the pipe size can be reduced.

My question: how can a smaller 3/4-inch domestic water main pipe be made to support a much larger 1-1/4-inch pipe inside the house?
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Old 08-31-2011, 02:26 PM
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The key is the velocity of the water, the larger 1 1/4 will lower the velocity and the pressure drop at fixtures in the house, say your useing 8 gpm, the flow through the 3/4 & 1 1/4 is going to be the same but the velocity, rate of flow through the 3/4 is going to be higher/faster than the 1 1/4. Hope this helps.
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Old 08-31-2011, 02:35 PM
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My house has a 3/4 main service and when I first bought it the reduced it down to 1/2, talk about pressure drop, you couldn't flush a toilet or run a fawcet without it affecting the rest of the house. I changed out the 1/2 to 1" mains and now no pressure drop throught the house.
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Old 08-31-2011, 02:36 PM
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plumber is right. From street to house is straight, no corners.
Each corner is a flow restriction and then pressure is reduced. Having a larger pipe inside the house offsets the effect of the elbows and T's.
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Old 08-31-2011, 02:48 PM
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don't know how it is in texas,but here you can run 3/4 up to 13 fixtures,then you must run 1 inch.I run all water service 1" to the house then drp to 3/4.unless of course it's a 15 bath house
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Old 08-31-2011, 02:50 PM
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Well for starters the tap fee will be lower for a 3/4 " than a larger tap size. However the 1.25" seems wayy too big.
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Old 08-31-2011, 03:05 PM
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Originally Posted by Eyeball View Post
I know some of you folks can easily explain this to me...

Plumber just did calculations for a home's water service, says minimums are:

(1) 3/4-inch pipe for domestic water main (from city main into the house),

and then

(2) 1-1/4-inch pipe inside the house until enough "units" fall off, then the pipe size can be reduced.

My question: how can a smaller 3/4-inch domestic water main pipe be made to support a much larger 1-1/4-inch pipe inside the house?
I've never seen 1 1/4" run in a house.

Have you considered running PEX?
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Old 08-31-2011, 03:25 PM
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Do you want to flush while your wife is showering? And maintain peace in the house
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Old 08-31-2011, 05:55 PM
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I've never heard of anyone running 1-1/4" in the house either. I have 1-1/4" for my sprinkler system mains, which is on well. From city meter I have 3/4" to house, then 1/2 throughout.
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Old 08-31-2011, 06:33 PM
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Typical 3/4 main line to 1/2 feeders...1 1/4"?..never heard of or seen it...
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Old 08-31-2011, 06:35 PM
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Maybe there's low pressure from the city.

Maybe plumber has 1 1/4" he needs to use up.

Guess it wouldn't hurt.

LOTS of guys going to PEX nowadays.
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Old 08-31-2011, 06:42 PM
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My curb service went in in May. It's 3/4 from the street to where it comes into the house - about 500 feet. All my indoor plumbing is 1/2 copper. More than adequate, more pressure than I need. "They" also made me install a pressure regulator and expansion tank.
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Old 08-31-2011, 07:45 PM
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It's always best to increase the volume of water and decrease the velocity of water. This eliminates "water hammer" and delivers more volume to the fixture like your shower head then increase the velocity exiting the shower head.
A lot of people misunderstand pressure for velocity, the speed water has to travel to equal volume.
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Old 08-31-2011, 08:15 PM
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Originally Posted by Eyeball View Post
I know some of you folks can easily explain this to me...

Plumber just did calculations for a home's water service, says minimums are:

(1) 3/4-inch pipe for domestic water main (from city main into the house),

and then

(2) 1-1/4-inch pipe inside the house until enough "units" fall off, then the pipe size can be reduced.

My question: how can a smaller 3/4-inch domestic water main pipe be made to support a much larger 1-1/4-inch pipe inside the house?
Most all installations require a pressure regulator. The 3/4" is on the high pressure side the 1 1/4" is on the low pressure side......
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Old 08-31-2011, 10:42 PM
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most residential here is 3/4 then stepped down to 1/2 inside I know in the city i have seen water services up to 6in going into some buildings
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Old 09-01-2011, 04:14 AM
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I hope you don't plan on using the 1 1/4" after the water heater. What your plumber is doing seems like mess. We bring in 3/4" from the street or well and then go to 1/2". Anything bigger than 1/2" from the w/h it takes longer to get hot water.
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Old 09-01-2011, 04:30 AM
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All houses that I have built or remodeled here have all had 3/4" 1/2". I have also never seen
1 1/4" used.
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Old 09-01-2011, 05:15 AM
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Where I am at, if you have more than 3 and less than 5 bathrooms the incoming line from meter to the home has to be 1" on a 3/4" water meter and at least 1" to the first bathroom,3/4" to the other 3. 6 Bathrooms to 8 the meter increases to 1" and the main line is no smaller than 1 1/4" with 1 1/4" main in the home. The last home we just plumbed had 7 baths, 1 1/2 meter, 1 1/2" main to home, 1 1/4" main to the first three baths then 1" to the others. The water heaters were large Rinnai's split system(2 units feeding 4 baths with 1" hot, and 1 unit feeding 3 baths 3/4hot)

If it was my place I would see if the meter can be changed to a 1" and run a 1 1/4" service.
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Old 09-01-2011, 05:22 AM
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Originally Posted by HTV View Post
It's always best to increase the volume of water and decrease the velocity of water. This eliminates "water hammer" and delivers more volume to the fixture like your shower head then increase the velocity exiting the shower head.
A lot of people misunderstand pressure for velocity, the speed water has to travel to equal volume.
Thats right. Have you ever used a Pressure washer? Some are putting out 2500psi. When the trigger valve starts to leak over time and drips, that drop is leaving the nozel at 2500psi. You could also have an eight foot diameter pipe with 1psi. I wouldn't want to stand under it when it is flowing. Flow rate and psi are like volts and amps.
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Old 09-01-2011, 06:29 AM
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http://www.hometips.com/buying-guide...-fittings.html
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