Confused about 1/2 or 3/4 inch valves

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flazoom

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I am going to purchase Grohe valves (1 thermostatic and 2 flow) for my master bath shower remodel. We were looking at 'aquabrass' as I posted in another question, but my wife saw the Grohe 'Allure' style and made her/our decision. I now need to decide on 1/2 inch versus 3/4 inch. I have 3/4 from the hot water heater to the bathroom, just up through the floor, which is then connected to 1/2 to the old shower valve and sinks. The 1/2 pipe to the shower is about 6 feet long and the connection to the 3/4 inch pipe is in the corner between 2 metal wall beams which makes it difficult to get to . (they use metal instead of wood 2x4s for the walls here in Florida. I plan to put in an 8x8 inch square showerhead mounted from the ceiling and a handheld mounted on a wall bar. I would like to be able to use them both at once on occasion. Is the 1/2 inch valve acceptable or should I go to the 3/4 inch? If I go for the 3/4,do I need to have the 6 foot of 1/2 replaced with 3/4? I tried searching previous threads but found differing opinions.
 

Peanut9199

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A 1/2" valve will give you less gallons per minute than a 3/4" would.
What you need to take in account is how many units you have feeding from your thermostaic valve.
Average 2.2 gpm for each, example 1 shower head 2.2 + 1 tub spout 2.2 + 4 body sprays 2.2 x 4 = 13.2 gpm
On a 1/2" valve at 45psi =10.8 gpm
60psi =12.8 gpm
75psi =14.0 gpm
On a 3/4" valve at 45psi =17.7 gpm
60psi =20.5 gpm
75psi =22.4 gpm

So as you see the higher pressure you have the more gpm it gives you but if you have lower pressure you get less gpm.
 

flazoom

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Thank you peanut9199 for responding,
AS you can tell I am a little lost on plumbing requirements.
I plan on running an overhead shower (7 or 8 inch) and a handheld in the shower. Separate volume controls for each. I expect that most of the time only one will be in use. Since each should be 2.5 gpm the total with both running should be 5.0 gpm? I am not sure of the actual PSI but I had a 'double' showerhead (two heads on a pvc 't') from the old wall feed and had plenty of pressure. Would these 2 heads be the same as the overhead and handheld? (I actually removed the flow restrictors on the old showerheads)
 

Geniescience

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sounds like you will be fine fine fine with 1/2" devices.

to answer your other question, about whether one can increase pipe size to 3/4" at any time at any place along the run, the answer is yes. So,if you want to, you can increase your pipe size to 3/4". And doing it is not bad for any reason. It might even decrease the pipe flow noise in the walls.

david
 

Jadnashua

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The spec sheets will tell you the normal volume of the heads. As long as the valve can supply at least that much volume (preferably a little more), then you will be fine. You should only notice a problem if the draw is trying to pull more water than the valve can supply.
 

flazoom

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Thank you geniescience,jadnashua and peanut9199,
I checked the specs on the shower head and hand held and both a 2.5 gpm. I also never noticed any wall noise from the pipes (but as I have aged I notice my hearing is not as sharp as it was - to much Rock and Roll in my younger years) I plan to go with the 1/2 valves. Good news since it will be a little bit cheaper.
 

fawcettwiz

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you should go with the 1/2"...shower heads, handshowers, and bodysprays are required to put out no more than 2.5 gpm. If you want to run the shower head (or rain head) and the handshower you will have 5 gpm of water. A grohe 1/2" thermostatic valve will handle that. General rule of thumb:
1 or 2 functions = 1/2" valve
3 or 4 functions = 3/4" valve
Also, if you use the thermostatic valve, make sure you have a volume control valve for each function...one for the shower head and one for the handshower.:)
 
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