The supply lines need to be sized properly the entire length for them to supply the shower. You can't run 1/2 inch pipe, go up to 3/4" pipe and have any impact on water volume.

To definitively answer the question of "what is properly sized?" you would need to have some more information about the shower head... such as it's flow rate, the distance from the main to the shower, etc. However, a cursory answer is that a 1/2 pipe isn't going to do that. In addition, you need to look at the capacity of the water heater to supply that amount of water and the ability of the drain to empty that amount of water. A shower head @2 gpm +2 body sprays @1.6 gpm each is moving about 5.2 gallons of water per minute. That would drain a 40 gal water heater in about 8-10 minutes.

Look, this whole fad of multiple shower heads is hugely wasteful of both water and energy.

oops. just noticed that you were looking at 4 body sprays, not two.

No way, no how are you going to do that with a 1/2 inch pipe.

Same issues only worse with drain and water heater.

With 4 body sprays and a shower head, you will have potential flow at a rate of about 12.5 gallons per minute if all are full open at the same time.

12.5 gallons per minute equates to about 8DFUs.

8 DFUs requires a minimum supply piping of 3/4".

Correction.

12.5 gallons per minute of flow equates to about 8 WSFUs (water supply fixture units).

DFUs (drainage fixture units) are used for drainage calculations.

Jakes calculations above are pretty close. For example, a Hansgrohe Raindance shower head is 2.5 gpm. Their body sprays are 1.6 gpm each. That works out to about 9 gpm total. This is the setup that we have, and with the Thermobalance valves (rated at 6 gpm) I can basically have one or the other but not both. In retrospect, I wish we had put in separate valves.

Also, consider a tankless hot water heater.

The water use is 8-9 gpm. That is a ridiculous amount of wasted water. Period.

Depending on water inlet temps, it would take two tankless heaters, including gas supply upgrades, to power that.

It's just stupid waste of resources.

:) The reality is that the body sprays get used about 2% of the time. The body sprays were more of a 'fun' thing than a basic requirement.

We have a single Rheem tankless driving the whole thing. I think it is rated around 7.5 gpm. The tankless also supports a spa tub and one other bathroom. I have a second Rheem for the rest of the house (another bath, the laundry, and the kitchen.)

> It's just stupid waste of resources.

Well, maybe it helps make up for the stupid 1.6 gal toilets that we are forced to install. I can't believe that 1.6 gal is enough to 'cleanse' the lines all the way to the street...

We have four Kohler body sprays (9l. per minute each) in our MB. They're running off 1/2" supplies with no problems. Other than testing it a couple of times, we've never used it in four years. Resale value only. I see now they offer low flow versions at 6l. per minute.

wws944 - really? "stupid 1.6 gal toilets". Aren't we talking 15 year old code. You'd think people would be over that. And your house is set up for upwards of 15 gpm of hot water (presuming your Rheems are equal sized).

I'm sorry but that really is a "stupid waste of resources" - as are body sprays. The good news is that it is a rare "Hummer" driver who actually uses body sprays regularly.

Sorry for the off topic rant but there is no shame in wasting resources anymore. I am building a high end custom home and would not do body sprays. I know that I would use them once and then conclude that they are a terrible waste of water (and the NG to heat the water). Now if I had solar hot water heater.... I can get over the water waste issue depending on where you live.

Wow! A mind IS a terrible thing to waste.
or as GWB said: "It's terrible when you lose your mind".

I think either quote would work in this instance.

DH: Gosh, the city is passing water rationing laws - what do they have against green lawns!

DW: Haven't you heard, the reservoirs are almost empty.

DH: I thought we won the battle with the farmers over who would get the water.

DW: We did, and for a while it was great that we could take a shower and wast six gallons a minute down the drain - If we need food, we just go to the store and get it. Why all the fuss about farmers and crops?

DH: And didn't we win the court battle with the state down river from us over water rights?

DW: Yes, but reservoir is still going dry.

DH: Hey, I got an e-mail from Danny, he said the fighting is pretty bad.

DW: I'm so proud our son is in the middle-east defending our patriotic right to drive a Hummer and waste huge amounts of energy to power our 100 gal water heaters. I can't imagine how inconvenient it might be if we had to live the same way as people in those third-world European countries.

DH: Which third-world European countries?

DW: You know, France, the United Kingdom, Germany

DH: I'm sure glad we don't live like them!

DH: Hey, I heard our neighbor, Bill, lost his job.

DW: What happened?

DH: Seems those danged foreign companies started building energy efficient cars and appliances and the company he works for couldn't get a government bailout so they are going out of business.

DW: That's terrible.

DW: It is terrible. You know I don't know how he's going to afford all that medication for his bad joints, diabetes, high blood pressure and such, just like you.

DH: Yep, the doc said I was morbidly obese - I didn't think that was very nice.

DW: I'm sure glad you don't have to get up off the couch too much.

DH: Me too!

Dual flush toilets are mandatory in Oz. Next come composting toilets. Before you know it, the gummit's gonna take away that soothing splash of a job well done. "From my cold dead a##" I say.

American Standard Cadet 3 - about $220. Very, very hard to plug up. I've had many 1.6's that would plug up but a decent one will not.

It is about the design not the amount of water. I've plugged many old toilets too.

Worthy - really? I mean is it that hard to pick which method of flush to do. I will have to say that they are expensive - but often that is a function of volume. Once the government mandates them, the price comes down. I hate government intervention but when it comes to preserving resources, it really is in our best interest. I am very conservative politically but that doesn't equal libertarian. No rules does not work.

Well, first off, how about everyone gets off their soap boxes and stops preaching what is a waste and what is not.

If you want body sprays, go for it. They are no more of a "waste of resources" than anything else we have the luxury of having (3,000+ sq ft homes, 60inch+ TVS, high cielings, multiple cars, whirlpool tubs, large refrigerators, etc).

In terms of water usage - yes, you can "get by" with 1/2, but 3/4 will make a very noticable difference. Keep in mind when these folks on here say your going to drain a water tank in such a time - your not using 100% hot water - its being mixed with cold - so will last much longer than what has been given here.

Okay, I'll admit my last post was out of bounds. Nonetheless, people need to understand that the decision to install multiple shower heads have a significant impact on the plumbing system as well as energy and water use.

A system that uses multiple shower heads needs to be designed to accommodate the flow rates. No, a 1/2" supply line generally will not do the trick. This could vary based on the flow rates of the heads. Low flow shower heads could change the equation.

In addition, the drain must be sized to be able to get rid of the water.

Finally, the water heater must be properly sized. Taking into account the cold water being mixed in, a 40 gal water heater will last about 10 minutes based on 140 deg hot water, 50 deg cold water, 105 degree shower and 5.6 gpm total on the shower heads. Normally you see an 80 gal heater for a setup like this.

People need to consider the full cost of their decision, including operating costs, when they decide to install multiple shower heads. And yes, it's very wasteful and we shouldn't be afraid to say so.