1/2" or 3/4" PRV?

[itsr-ent]

I need to install a PRV after my water meter to drop the 120psi city pressure down to 60-75psi. I have a 1" copper water service, the water meter, and then 1/2" copper in the rest of the house (including to the water heater...no 3/4" anywhere).

I was told that a 3/4" Watts PRV has less head loss than a 1/2" Watts PRV (so it's more than just the connection sizes being different). I can use a 3/4" PRV with 3/4" to 1/2" copper adapters if that would be best...I'm just not sure.

Should I go with the 3/4" PRV or just stick to the 1/2" PRV?

 

[Terry]

If it's a one bath home, then 3/4" would do. If it's two or more bathrooms, then you should go with the 1".
At some point, you will want to run 3/4" to the water heater.
I run 1/2" to two plumbing fixtures, not three. Even with a one bath home, you would have up to six items.
A bathroom would get 1/2" for the tub and lav, and 3/4" for the tub, lav and toilet.

 

[Sponsor]

 

[itsr-ent]

If it's a one bath home, then 3/4" would do. If it's two or more bathrooms, then you should go with the 1".
At some point, you will want to run 3/4" to the water heater.
I run 1/2" to two plumbing fixtures, not three. Even with a one bath home, you would have up to six items.
A bathroom would get 1/2" for the tub and lav, and 3/4" for the tub, lav and toilet.

It is a (small) one bath home. I don't have any issues at all right now with 1/2" copper, so I haven't made a plan to upgrade to 3/4"

You think the 3/4" PRV is definitely worth it over the 1/2" PRV though?

Also, do you mean a half bath (lav and toilet) would get 1/2" copper but a full bath (tub/shower, lav, toilet) would get 3/4" to the general area and then 1/2" to each of the fixtures? I want to make sure I understand in case I do want to upgrade to some 3/4" copper at some point.

 

[hj]

Head loss is caused by the velocity through the PRV and if you only have 1/2" piping, then the velocity will be about the same between the two PRVs.

 

[Terry]

You think the 3/4" PRV is definitely worth it over the 1/2" PRV though?

Also, do you mean a half bath (lav and toilet) would get 1/2" copper but a full bath (tub/shower, lav, toilet) would get 3/4" to the general area and then 1/2" to each of the fixtures? I want to make sure I understand in case I do want to upgrade to some 3/4" copper at some point.

I would go with the 3/4" for the one bath home. Right now you're running 120 PSI. Drop the pressure down and the 1/2" line won't carry as much water.
A half bath can have lav and toilet off of one 1/2". Or a full bath can have the tub and lav on one 1/2".
Adding the toilet to the cold means that the 1/2" is trying to do too much.

I can't recommend installing a PRV that is less then what plumbing code wants.

 

[Wrenched]

Hey itsr-ent,

I don't think it will make much of a difference at the faucet if your house is plumbed in half-inch, and the pressure drop across the PRV is 20+ psi.

A 3/4" PRV might have ~20% less head loss, but that's irrelevant going from 120psi to 60 psi - the PRV is set based on downstream pressure, and the difference between 12psi or 15psi head loss at 10gpm isn't noticeable on that pressure differential.

That said, the price difference isn't much( a 3/4" PRVmay even be cheaper from some suppliers), and the 3/4" PRV is better value. You will notice a large difference between 120psi and 60-70psi, and may want to re-pipe in 3/4" in the future (e.g. when the piping starts to leak. ).

 

[itsr-ent]

Hey itsr-ent,

I don't think it will make much of a difference at the faucet if your house is plumbed in half-inch, and the pressure drop across the PRV is 20+ psi.

A 3/4" PRV might have ~20% less head loss, but that's irrelevant going from 120psi to 60 psi - the PRV is set based on downstream pressure, and the difference between 12psi or 15psi head loss at 10gpm isn't noticeable on that pressure differential.

That said, the price difference isn't much( a 3/4" PRVmay even be cheaper from some suppliers), and the 3/4" PRV is better value. You will notice a large difference between 120psi and 60-70psi, and may want to re-pipe in 3/4" in the future (e.g. when the piping starts to leak. ).

Thanks for the info. The 1/2" PRV and 3/4" PRV from the supplier I use are both the same price. The 1/2" would be nice just because I already have a good stock of 1/2" fittings to install it. Like you said, I'm worried the change from 120 to ~70 is going to be drastic, so I'm definitely willing to go with the 3/4" PRV if it would make any sort of noticeable difference (which it sounds like it will not).

I've thought about re-piping in 3/4", but honestly my water meter is located in the basement directly under the single bathroom. Once the 1/2" pipe gets to the ceiling, the tub/shower, lav, and toilet are all within 10 feet. The water heater also isn't more than 10 feet from the water meter/bathroom. Some of the runs to each fixture are so short, it would be difficult to re-attach to them from the new 3/4" pipe. The only thing far from this area is the kitchen sink, which is about 25 feet away.

 

[itsr-ent]

Anyone have experience with the Honeywell DS06 PRV? http://www.supplyhouse.com/Honeywel...T-DialSet-Pressure-Regulating-Valve-Lead-Free

The fall off seems less than the Watts LF25AUB-Z3. Closer to the really expensive Watts U5B-Z3 models.

There's also a 1/4" gauge tap built-in, and the double union model is readily available for a great price. Can't find many reviews though...everyone seems to go with the Watts LF25AUB-Z3.

EDIT: I also like that the Honeywell goes up to 90PSI, which would let me set it at 80. The Watts (unless you order the higher pressure version) adjusts up to 75.

 

[itsr-ent]

I went with the 3/4" Watts LF25AUB-Z3 simply because it's what everyone seems to stock around here. I ordered it online, but if it fails I wanted to make sure I can just grab one locally. Installed it over the weekend and so far so good. For ease of replacement, I used a female 3/4" to male 1/2" ProPress adapter with the included inlet union. On the outlet, I added a 3/4" brass nipple, 3/4" to 1/2" brass reducer coupling, and then a male 1/2" ProPress union. If I need to swap out the PRV, I can undo both unions, swap the brass nipple, reducer, PP union assembly over to the new one and re-install.

I set the pressure at 70psi and my expansion tank at 72psi. It's still a big change from 120-130psi, but definitely usable. The shower/sink/toilet/washing machine are all a lot less "violent" now.

Pressure drops off about 5-8 psi when running the water in 2 places (flushing the toilet and using the sink), which seems in line with Watts' fall off diagram. Doesn't cause a big issue.