Sizing Water Supply

[claytoncarney]

First attempt calculating water supply size.

Background:

• Single story family residence
• Built in 1955
• All building piping is 1/2" galvanized steel
• 3/4" meter/service
• Meter located 40' from building, 3' below floor level
• Static pressure at floor level is 65 psi
• Supply line from meter to building replaced with 3/4" pex-a 5 years ago

Continually dropping flow rates (likely due to corrosion/hard water scaling) suggest replacing all building plumbing. Currently considering pex-a.

Looking at UPC Table 610.4, I see two entries which might be applicable:

• 3/4" meter/service and 3/4" building supply
• 3/4" meter/service and 1" building supply

Questions:

• Am I interrupting the table correctly: can you connect a 1" building supply to a 3/4" meter?
• If so, would it make sense to use a 1" building supply when the line between the meter and the building is only 3/4"?

I ask because initial WSFU calculations (using 75% rule) indicate a 3/4" building supply is inadequate (Hot 9.375 FU and Cold 15.875 FU, totaling 25.25 FU for the building supply).

 

[Twowaxhack]

Are you keeping your 3/4” water service from the meter to the house ?

If so just run the hot/cold main lines in 3/4” pipe and drop to each fixture with 1/2”. 3/4” to the water heater.

 

[claytoncarney]

Current plan is to keep 3/4" meter/service. And, yes, all fixture supplies (except water heater) would be 1/2".

Table 610.4 lists 3/4" meter/service with 3/4" supply up to 17 FU. However, it lists 3/4" meter/service with 1" supply up to 33 FU, which is adequate for 25.25 FU.

It just isn't clear to me: is connecting a 1" supply to a 3/4" meter/service a valid configuration (especially if the the meter-to-building line is only 3/4")?

 

[Twowaxhack]

Current plan is to keep 3/4" meter/service. And, yes, all fixture supplies (except water heater) would be 1/2".

Table 610.4 lists 3/4" meter/service with 3/4" supply up to 17 FU. However, it lists 3/4" meter/service with 1" supply up to 33 FU, which is adequate for 25.25 FU.

It just isn't clear to me: is connecting a 1" supply to a 3/4" meter/service a valid configuration (especially if the the meter-to-building line is only 3/4")?

You can install the 1” but I wouldn’t waste my money. It’ll offer less pressure loss and slower flow rates. IMO it’s not needed if you have a 3/4” service pipe from the meter to the house. 65psi is good pressure.

Consilt your local plumbing inspector for guidance if you’re trying to satisfy a local authority.

 

[Twowaxhack]

You may need to upgrade your main if you want to be in compliance.

 

[claytoncarney]

Thank you for helping. I don't intend to do this myself; just trying to understand the basics. UPC table indicates that 1" supply supports 90% more FU than 3/4" (if my understanding is correct). I assume a plumber or inspector would run the same calculations and conclude a 3/4" building supply is inadequate. Upgrading to 1" meter/service and replacing the meter-to-building line with 1" is an expense I hope to avoid.

 

[Twowaxhack]

Most 3 bedroom two bath homes here have a 3/4” water service if built before 1985. After around 1985 1” was used.

At the first outlet the cold was reduced to 3/4” and the hot supply matched the outlet of the water heater and typically that’s 3/4.

Good luck to you

 

[claytoncarney]

This is 2 bedroom, 1 bath.

I discovered that I did the calculation wrong. I was not aware of UPC 610.9 (No branch piping shall exceed the total demand in fixture units for the system computed from Table 610.3). I was combining hot and cold FU, instead of using total demand in fixture units (15.875). With that correction, a 3/4" meter with 3/4" supply is adequate. Problem solved.

 

[LostQ]

This is 2 bedroom, 1 bath.

I discovered that I did the calculation wrong. I was not aware of UPC 610.9 (No branch piping shall exceed the total demand in fixture units for the system computed from Table 610.3). I was combining hot and cold FU, instead of using total demand in fixture units (15.875). With that correction, a 3/4" meter with 3/4" supply is adequate. Problem solved.

Is this to code? I am super confused. I read your post and had the same issues as you. After adding the hot and the cold FUs, my 1" pipe was not good enough. Am I not supposed to add hot and cold, but just use the larger number!? Thank you!