flow question

the pelon

the pelon

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I am installing new walk in shower converted from a tub/shower combo. I purchased a Grohe 3/4" Thermo valve. After completing the tear out today, I am having a hard time finding the 3/4" trunk lines to feed the new valve. I have a 2 story house so they may have switched to 1/2" between floors. My plan is to have a hand shower on one wall and a regular shower on the other wall both controlled by volume control valves. My question is, will a 1/2" Therom valve have enough flow to run both showers if I cant locate the 3/4" lines. The shower will be approx. 4'x6'. Thanks in advance, Pete
 
Without knowing the pressure and the flow rate, no one will be able to give you a definitive answer. So maybe yes, probably no is as close as you're gonna get at this point. Personally, I'd swap out the valve for something with 1/2" connections.
 
do you need the pressure and flow rate of my incoming house water or of the valve it self? It is not possibe to use a 3/4 by 1/2 " adapter and stay with the same valve? Thanks, Pete
 
Determining the pressure is fairly cheap and easy - pick up a pressure gauge at a plumbing supply or a big box store for about $10 and screw it onto a hose bib (outside or at the washing machine, or the WH drain - or elsewhere if you buy adapters).

A 1/2" pipe can probably successfully flow about 6-8 gallons per minute. A 3/4" one can do significantly more, but it depends on the pressure. A showerhead can be NGT 2.5 gallons/minute, so often, two could be run from a 1/2" supply, but you won't know until you can determine the pressure.

Yes, you can use an adapter to go from the 1/2" supply lines to your valve. A 3/4" valve is often quite a bit more than the 1/2" version, and without 3/4" inputs, is kind of a waste. But, with restocking costs, it may be a wash.
 
is running a 3/4 valve in an area that only 1/2" will support just a waste of money but still will work or is the 3/4 not functional?? Knd of like putting premium gas in a ford pinto, the car will run fine but you could get by with just putting in regular. Nice analogy eh, anyone out there still have a Ford Pinto????
 
Upsizing the valve or pipe at the valve body will make no difference to the flow rate at that point. Like I said, maybe the valve will work ok, maybe not. Quite a few of those valves that are tapped 3/4" need a lot of flow to function properly. You would hate to go to all the trouble of installing it only to find the water barely trickling out the shower head. Pressure alone is not an indicator. You can have lots and lots of pressure and no volume. What you're looking for is volume.
 
Upsizing the valve or pipe at the valve body will make no difference to the flow rate at that point.

Iam confused.... why wouldn't increasing the line from 1/2" to 3/4 increase flow? and wouldn't a 3/4 valve increase flow as opposed to a 1/2 valve?
 
If you can increase the pipe size all the way back to the main it will make a difference. Increasing it at the valve will do little to nothing, including increasing the valve size. Most of the volume loss is still within the 1/2 in feeder line running up from the basement along with the friction loss.
 
I appreciate your patience with me nhmaster. The main feed from the street into the house is 3/4". I can tap into 3/4" with significant more tear out, to make sure that I get proper flow, volume and pressure to my 2 shower heads.The 3/4" splits to 1/2" approx. 5' from where my shower valve is going to be located. I was hoping that short of distance of 1/2" would not reduce the flow that significantly to the 2 shower heads. Also, I am on the fence about using 1/2 adapters on my 3/4" valve or scrap the valve and get a new Grohe 1/2" valve. thanks in advance, Pete
 
so HJ, you are saying go ahead and use the 3/4" valve and just put in the adapters? Will I have enough flow for 2 shower heads using the 1/2 line that feeds the valve? so it sounds like a 3/4 valve in residential use is way overkill????
 
the pelon said:
so HJ, you are saying go ahead and use the 3/4" valve and just put in the adapters? Will I have enough flow for 2 shower heads using the 1/2 line that feeds the valve? so it sounds like a 3/4 valve in residential use is way overkill????
Click to expand...

Typically the 3/4" valves are used in shower systems that have multiple heads...
I refer to them as "Car Washes"

Yea I think they are overkill and a waste of water...
 
dont mean to beat a dead mule here fellas, but I am running multiple shower heads, (2) and dont want to put in time money and effort and have poor flow to both heads. would the advice be get 3/4" to the valve at "all costs" to ensure proper flow or would the existing 1/2" be sufficient to run both heads. It sounds like the 3/4" valve I purchased will work with either 1/2 adapters or, obviously, with 3/4" pipe if 3/4" is necessary the run the 2 shower system. Appreciate your patience, just trying to get this right before I spend the thousands of dollars on the remodel. Thanks, Pete
 
3/4 valves

The only reason for the 3/4" valves is to get larger internal ports, but if you check them, you will see that their areas are nowhere near equal to the size of a 1/2" copper line, just as 1/2" valve ports are very small compared to the 1/2" copper line feeding them.
 
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