# Seeking input on replumbing with Pex-A, adding water heater booster, and a recirc line



## Movingshrub (Jun 12, 2017)

I've got a 1960s house. I'm renovating three bathrooms, one after another. The house has original copper pipe for the potable water supply. Due to the amount of pipes that will move during the renovation, I'm planning to go scorched earth, remove the original copper pipe ,and replace with Uponor Pex A.

I need a sanity check on my pipe sizing. The meter is 3/4", and I have 80psi where the water enters the house.

I calculated a total of 33 fixture units with UPC and with UPC a total of 15.7 water supply fixture units + three hose bibs. I estimated a pipe length from the meter to the furthest fixture between 125-150 feet using google maps. The way I'm reading UPC Table 610.4 is that with a 3/4" meter, at 80psi, with a length of up to 150ft, and 33 WSFUs, I need to use 1" pipe for the building supply and branch, and potentially jump to 1.25" pipe if the distance is longer than 150 feet. I am surprised because there isn't a single piece of 1" pipe in the house. With the IPC, Appendix E, I'm assuming a velocity of 10ft/s or less per Uponor's Design manual for 60F water. There isn't guidance on GPM for hose bibs. The calculations on the fixtures where there is guidance put me at a floor of 20GPM, in terms of design requirements. As a result, of hose bibs not being explicitly assigned a GPM in the IPC, I'm going to assume a total requirement of 20-30GPM, which puts me solidly in the 1" pipe size, but approaching 1.25"

What am I missing here? Was the house pipe undersized all along? Did I do the math wrong? Did the code change over time on this?

In terms of fixtures:
Three Toilets
Four Lav Sinks
Two bath/shower
One walk-in shower
One washing machine
One Dishwasher
One Kitchen Sink
Three hose bibs

I wasn't sure how to capture the refrigerator ice maker demand. I also am considering the potential for capacity in the event a second shower head is added to any bathrooms and/or if a laundry sink is added as well. None of these few potential items were included in the WSFU or FU calculations.

Separate from the math calculations, I' adding a Stiebel Eltron on-demand 15kw electric heater as a feeder into my hot water tank. That should give me around a 50F rise to basically pre-heat the water going into the tank. I need surge capacity for when the kids take back to back showers, versus forever hot water. In addition, no gas service to the house, hence the electric plan.

Lastly, I'm planning to use a Grundfos recirc pump, with a redicated recirculation line to reduce the wait time for hot water. Assuming I didn't butcher the head calculations, I'll be going with an Alpha2 15-55SF/LC. I'm aiming for a 5F delta T for 120F temp water.

I'm open to input on all of the topics covered here.


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## g-man (Jun 15, 2017)

3/4 copper = 1in pex

The id of pex is that smaller. Bigger Id is better without any negative than your wallet.


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## Movingshrub (Jun 12, 2017)

g-man said:


> 3/4 copper = 1in pex
> 
> The id of pex is that smaller. Bigger Id is better without any negative than your wallet.


I did check the ID. My understanding is that Uponor Pex-A is treated equivalent, size-wise, to copper since it can handle higher velocity.

Even if I were to just replace the existing stuff with copper, I'm so confused why the sizing recommendations are larger than my current setup, without any changes to the layout. I'm the second owner of the house and haven't seen any major changes to the house that are modifications to the original.


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## g-man (Jun 15, 2017)

I don understand all of your calculations. A hose bib wont do 20-30gpm. There are a lot of restrictions thru the valve.

A toilet will use ~3gpm. A shower head used to be 3gpm, but I think now they are 1.5gpm. Washing machine is your worst offender at around 5gpm. You will need to be doing multiple of these at once to the gpm high enough that friction losses x distance can cause issues.


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## Movingshrub (Jun 12, 2017)

g-man said:


> I don understand all of your calculations. A hose bib wont do 20-30gpm. There are a lot of restrictions thru the valve.
> 
> A toilet will use ~3gpm. A shower head used to be 3gpm, but I think now they are 1.5gpm. Washing machine is your worst offender at around 5gpm. You will need to be doing multiple of these at once to the gpm high enough that friction losses x distance can cause issues.


I worded that sentence poorly. I'll edit the OP.


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## Movingshrub (Jun 12, 2017)

Using the IPC, I'm tracking a total of 15.7 WSFUs, resulting in a ball park of 17.5GPM.

Cold	Hot	Total
Bathroom Group	2.7	1.5	3.6
Bathroom Group	2.7	1.5	3.6
Bathroom Group	2.7	1.5	3.6
Lav Sink 0.5	0.5	0.7
Washing Machine	1.0	1.0	1.4
Kitchen Sink 1.0	1.0	1.4
Dishwasher 0	1.4	1.4
WSFU 10.6	8.4	15.7
GPM 14.6	13	17.5
+Three hose bibbs 
Leading to my assumption of 20-30 GPM


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## Ware (Jan 28, 2017)

For a normal size home I'm not sure if I've ever seen anything bigger than 3/4″ trunk and 1/2″ branches.


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## Movingshrub (Jun 12, 2017)

Ware said:


> For a normal size home I'm not sure if I've ever seen anything bigger than 3/4″ trunk and 1/2″ branches.


Which is why I'm assuming I must be missing something in the code.


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## g-man (Jun 15, 2017)

Again, to get to 20gpm, you are adding all of those groups. Gallons per minute (GPM), only happens when you open the faucet. When the faucet is closed, GPM=0. I would design for 5gpm, which 3/4in copper or 1in pex would be enough. My house was built with 3/4 pex. It works but i sure would like 1in pex for the irrigation.


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## Movingshrub (Jun 12, 2017)

No arguments from me. I'm following the calculation directions in the code, at least think I am. It seems oversized which is what drove my post - Am I messing up the calculation? Is the code design overkill?

For irrigation, I went 1' meter and 1.25" pipe, so no irrigation water going through the house.


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## jayhawk (Apr 18, 2017)

I respect your engineering level detail. You're out of my pay grade there. 3/4 line hold a LOT more water than a 1/2 line, not a help to wait time. 
Great choice - uponor ...love the connection and bend (less fittings)

The 80 psi, doesn't it get down regulated by the PRV? (Like to the 50s)


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## Movingshrub (Jun 12, 2017)

jayhawk said:


> I respect your engineering level detail. You're out of my pay grade there. 3/4 line hold a LOT more water than a 1/2 line, not a help to wait time.
> Great choice - uponor ...love the connection and bend (less fittings)
> 
> The 80 psi, doesn't it get down regulated by the PRV? (Like to the 50s)


I regulated it down to 75psi. I just don't want it at 100+.


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## Captquin (Aug 22, 2019)

You're in AL, so an electric water heater will be fine. Not sure I understand why you're piggybacking with a tank though. For not much more, you can upsize the tankless and get rid of the tank. It'll save energy and give you more space.

Completely agree on the 1" PEX.

Lastly, I'd suggest visiting your local Ferguson, etc. if you haven't already. You'll appreciate dealing with people who know what their talking about and have everything you need rather than dealing with a Big Box.


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