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Thread: Need advice for installing three body sprays

  1. #1
    DIY Member jerome7's Avatar
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    Default Need advice for installing three body sprays

    Hello all

    I am remodeling my bathroom and I want to install 3 body sprays to my shower stall. I noticed my shower valve is connected to 1/2 inch hot and cold water input. I took a measurement at the shower head and got 68PSI (water is not running). Do you see any problem w/ this setup? Some people recommended me to upgrade to 3/4" pipe to get better flow. How much better will it get and does it mean I will deplete the hot water tank at a faster pace?

    Thanks much

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    In the trades Dana's Avatar
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    Yes, adding more sprays depletes the tank faster.

    At 68psi you'd still be getting "pretty good" gallons per minute (gpm) through half-inch, but if it's a long run it could become the limiting factor. Add up the rated gpm numbers for the heads (including the main head), and tell us the length of run (including the number of ells) between the water heater and the shower.

    Short of installing a newer bigger tank with more storage volume/burner, for about $500-600 in hardware you could install a drainwater heat recovery heat exchanger, feeding both the water heater's & shower's cold inputs, effectively doubling the "apparent volume" of the water heater while cutting the fuel use in half. NRCan lists 3rd-party tested efficiency at a standard 2.5gpm flow rate, but note that at higher flow rates you'll get somewhat lower net recovery efficiency, but even at 6 gpm a unit that tests at 50% @ 2.5gpm would be delivering about 40%, with a very significant boost in apparent capacity. In general, within a product line the longer & fatter the heat exchanger, the higher the efficiency. It needs to be installed vertically, so it's not going to be a solution for first floor showers on slab-on-grade houses.





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    Retired Defense Industry Engineer jadnashua's Avatar
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    Depending on the mix of hot/cold, a 1/2" pipe will normally only supply in the order of 5-6gpm. So, add up the demand from the specs on the sprays you want and see where you stand. You may need not only bigger pipes but a bigger valve. Check the specs on your valve, too. To be able to maintain the water pressure you have, you need to be able to supply more water than they can output (or at least match the in/out). The water pressure on a soda straw will be the same as in a fire hose when there's no flow...the size of the pipe does not determine the static water pressure - the system supply does that; it only determines the flow available.
    Jim DeBruycker
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    In the trades Dana's Avatar
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    We're talking only 4 heads here, and a fairly hefty 68psi (static), so it just MIGHT cut it with 1/2" if it's a relatively short run, since you're probably looking at ~2-2.5gpm per head, or ~10 gpm total. (Mind you, that drains a 50 gallon tank pretty fast unless you have drainwater heat recovery.)

    At 10gpm it's losing about 0.8 psi/foot. ("equivalent feet", including equivalents for all ells, etc.) If it's only 25' you might still get there, since you'd be losing only (25' x 0.8=) ~20 lbs, so you'd have over 40 psi at the showerheads. If it's 100', probably not. Most shower head gpm volumes are specified at 80psi, but still deliver the bulk of that flow rate at 40psi, or even 30psi. Below 30psi you may have issues with how far the sidesprays can squirt though. Measure it up, look at the gpm @ 80 psi numbers for the heads, add it all up and use this nomograph to determine if you're in the ball park or not.
    Last edited by Dana; 05-02-2013 at 10:42 AM.

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    DIY Member jerome7's Avatar
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    The body sprays that I am getting use 1.6gpm at 80PSI. The water volume is also adjustable on this model. My shower is on the second floor and the hot water tank is on the first floor. I cannot tell how the pipes run thru the house but the horizontal distance between the tank and the shower valve is about 25ft.

    I dont understand few points about the calculation.
    1) what distance are we estimating? between the shower valve and the water tank? shower valve to the main supply?
    2) why do we need to estimate the PSI loss? we already know we have 68PSI at the shower head. Isn't the PSI loos already accounted in that 68PSI?

    Not sure if we need to account for this, but we have a water softener and due to it's location, we had to run 2 14ft tubes to the main line.

    Thank you everyone for your help. Ohhh my head hurts

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Static water pressure is useful, but working pressure (while there's a demand) will vary depending on the size of the pipe and the frictional losses getting it from point A to point B. The bigger the pipe, the fewer frictional losses there are. The fewer the changes of direction, the less friction (one reason pex can help compensate since it generally has far fewer joints or changes of direction than a pieced together rigid pipe system). Think of it this way...run your garden hose with no nozzle on it. The water will only project so far. Put a restriction on the end (like your body spray), and it can flow further since you're restricting the flow. But, now split that outlet to many sprinkler heads, your static pressure is the same, but you will often only get a trickle out of the sprayer heads, and the one furthest from the source may not get any. To work well, your supply needs to be able to deliver MORE water than the heads can disperse or your working pressure will drop. FWIW, most 1/2" valves will NOT provide much more than 6-7gpm (and some less). To get more, you generally need to go to a 3/4" valve (which can add considerably to the costs!).
    Last edited by jadnashua; 05-02-2013 at 05:40 PM.
    Jim DeBruycker
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    DIY Junior Member wmichsabre's Avatar
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    So is it best to run 3/4" pipe all the way until just before the fixture? Where is the optimal place for the reducer, since the fixtures (body sprays in this case) are 1/2"?

    Should the pressure balancing loop be 3/4" or 1/2"?

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    The less you ask a 1/2" line to do, the easier it is for it to maintain maximum volume and pressure. Assuming all of the body sprays will come off the loop, then you want the loop to be able to easily supply them all and reduce at the point of use. This will make no difference if you are using a 1/2" valve, since that will likely be the limiting factor. A larger line will take longer to purge any cold water and to warm up, though. There are advantages and disadvantages and you have to weigh the good and bad, then make a decision. Does the installation manual say anything?
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    You need to add up both the length of the pipe, and the equivalent lengths of the fittings the water flows through, and apply that to the pressure drop with flow nomograph.

    If you have three heads rated 1.6gpm @ 80psi (4.8gpm total), plus a 2.5gpm rated full-flow showerhead, that adds up to about 7- 7.5gpm. Derated for 40psi operation they'd be drawing maybe ~5gpm total, and it would still feel like pretty good flow.


    Assuming you have few restrictions on the in-bound side of the hot water heater that means you can tolerate about a (68psi - 40psi=) 28 psi drop at 5-6 gpm. Looking at the nomomgraph, at 6 gpm half inch copper loses about 0.3 psi per foot (or equivalent-foot), at 5 gpm it loses about 0.2psi/foot so if your equivalent foot limit is about (28psi/0.3 =) 93' to (28psi/0.2=) 140'.

    Your horizontal run is about 25', your vertical is probably another 15-20', but let's call it 20, that's 45' of pipe. Every ell only adds ~1' every branch tee is ~2' of equivalent length, it would take a LOT of fittings between tank & shower head to stretch that to 93'.

    Valves will add some more equivalent length, but the type of valve matters. A straight 1/2" sweat-fitted gate valve adds almost no equivalent feet beyond it's physical length, but an angle valve adds ~10', and a globe valve as much as 20'.

    So, assuming you have something like 5 ells and 3 tees, and a globe valve you'd be looking at (5 x 1) + (3 x 2) + (10 x 1)= 21' of additional length to add to the 45' of pipe, and you're still in pretty good shape. But count the fittings& valves, measure the real pipe lengths, and run your own arithmetic.

    If there was ever an appropriate & cost effective purpose for these beasts, its for gusher-showers with side sprays, since it delivers as much or more showering capacity to a 50gallon standard-burner gas fired tank than up-sizing to a 75KBTU/hr. Most decent-sized units are set up with 3/4" plumbing on the potable, and since the unit itself has some real length to the slinky-coils it's safer to just replumb it all with 3/4" plumbing, which would make it, without question. At your 5-6 gpm realistic flows, a better-grade 4" x 48" heat exchanger would be delivering over 40% heat return, and a 4" x 60" would be returning about 50%. With a standard 50 gallon gas-fired tank at 6 gpm shower flows you've got at best ~7 minutes of showering time before the temps plummet, but adding the drainwater heat recovery doubles it, with a much softer/slower transition on the temperature drop as the tank nears depletion.

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    Asking a copper pipe to supply to run faster than about 5-6 fps is just asking for long-term problems. Obviously, the larger the pipe, the more gpm that is. Restrictions cause the velocity to increase (venture effect) then decrease once the diameter is restored. This causes turbulence that can actually erode the metal away, and eats up the ultimate gpm because of the frictional losses. While a shower system is not a constant use thing, exceeding 5-6 fps water velocity in the supply piping is asking for problems down the road, and performance hits in the meantime.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member jerome7's Avatar
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    Thank you for the explanation. It's a great way to visualize it and helps quite a lot to understand. Looking thru the valve hole I can tell the hook ups are 1/2" but it might be bigger pipe leading to bathroom. I will know more once I take down that wall.

    I see that hot water supply is a big concern. Can the heat exchanger be installed "locally"? By locally I mean in the subfloor near the drain or in the wall near the body spray? If I have to tear down more of the house, it won't be an option. I would then prefer to use a tankless water heater.

    How expensive is such heat exchanger?

  12. #12
    Retired Defense Industry Engineer jadnashua's Avatar
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    The waste water heat exchanger works far better if it can be installed vertically...essentially, the drain water from the shower must drop down through it, so it must be under the shower, or somewhere where that drops vertically in the wall before it drains out to the sewer. Then, the cold water supply runs through the heat exchanger on the clean (potable) side to pick up heat as the water drains, preheating the water and lessening the load on the WH and the amount of full hot needed. When water drains through a vertical pipe, it tends to fall in sheets in contact with the inside wall of the drain, which maximizes the surface area of the heat exchanger. Horizontal heat exchangers are not anywhere near as efficient, since gravity would almost always leave most of the pipe surface uncovered by the flowing waste water. So, unless you have a vertical drop somewhere where you could insert one, it isn't in your future. A few more things to keep in mind, because the incoming water to a WH is cold, and it mixes with what's already in the tank, you will never be able to use the entire volume of the tank that started at a fixed temp...it will start to cool off near the end. You should only count on getting in the order of 70-75% of the volume of any WH before it starts to cool off. RE tankless, in Gilroy, it's possible that your winter, incoming water temps could end up quite low. A tankless system's output decreases significantly as the incoming water temp drops. The big numbers on their advertising are for typical, national summer water temps. Expect maybe a 70-degree rise at the stated flow rate. If your water temp can get to near freezing like it can where I live in the winter, that's 100-degrees at best unless the flow rate drops. You need to read the fine print carefully...it might work fine in the summer, but not in the winter. The joy of endless hot water can be a very expensive operation, and very frustrating unless you understand and plan for your actual needs under real conditions.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the trades Dana's Avatar
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    If you buy through EFI (link found on my first post) you can get a decent ~53% efficiency 4" x 48" for about $600, (delivered), which is far cheaper than any manufacturer's buy-direct or the Home Depot online price at any similar performance point. (You can open an account with EFI over the phone with a credit card to get their listed price, or at least that was my experience a few years ago. I've bought other goods from them since- they're a decent vendor, good communication, no markup on shipping, always very professional.)

    They need to be mounted vertically for soapy drainwater to have sufficient surface tension to spread out for good heat transfer. Anywhere downstream of the shower's drain flow is fine, as long as it's dead-straight vertical. They also need to feed both the cold-side of the hot water heater AND the cold side of the shower to deliver the rated performance. It's usually easiest to plumb it in next to the water heater, but it'll still work from 50' away, if need be.





    A 199,000 BTU-in condensing tankless can only be counted on for about 190,000 BTU/hr out. At 6 gpm you're running about 3000 lbs/hr, so the max temperature rise you can get from incoming water to shower-heads is 190,000/3000= 63F. With a 105 F showering temp, that means the lowest incoming water temp you can tolerate is 42F. If you like killer-hot 110F showers you'd need at least 47F incoming water.

    But if you add the drainwater heat recovery it just won't matter what the incoming water temp is- even 32F glacial runoff would be fine, since it would be raising the temp to about 70F ahead of the water heater, giving it HUGE margin on burner output. It also lowers the pressure drop you'd normally see across the tankless a bit too, since it's using proportionally less tankless flow, and higher cold-side flow. The difference in pressure between the hot & cold due to the heat exchanger of a tankless is sometimes an issue for anti-scald mixer valves, particularly when run at higher flow. A condensing tank heater doesn't have this issue, and even the 76,000BTU/hr Vertex tank is enough burner to run nearly-endless 5gpm showers when used in conjunction with drainwater heat recovery. The 100,000 BTU burner version would be as endless in your application as the tankless, with none of the tankless quirks, and fewer maintenance issues to boot.

    If the heat exchanger needs to be tucked into a stud bay, the 3" x 60" versions can usually be made to just barely squeak in with a bit of adjustment on wallboard thickness, but it's tight. A 2" x 60" will fit in a stud bay easier, but only delivers ~45% efficiency at 2.5gpm, maybe 35% @ 6 gpm. (Which is enough, but not the slam dunk a bigger/fatter version would be.) Where the existing drain runs from the second floor down to the first is the most likely placement, unless you have a full basement to work with too. Simply feeding the whole-house cold distribution with the heat exchanger works, but it means the cold water draws from other taps will also be 70-75F whenever someone is in the shower. (Which is room, temp, eh? Most people will tolerate room temp cold water for most uses, since that's the temp the water in the cold water pipes stagnates to, no matter what the incoming water temp is.)

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    DIY Member jerome7's Avatar
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    Wow, that's a dream system you have there. It is also so neat how you connected all this stuff. Is it in a basement?

    After the demolition, I can see the drain is running down along an exterior wall. My kitchen cabinets and counter top are in front of the wall, thus I don't have access to the drain pipe

    On another topic, I'd like to install a handheld shower bar (and diverter) on the wall that is adjacent to the shower head. Thus the pipes need to do a 90 degree turn. How can fit the pipe in there given the studs blocking access to the corner? On the picture, the shower valve is on the wall w/ the yellow insulation and I'd like to mount the handheld bar on the wall w/o the insulation. There are 3 studs (2x4).

    My shower was done in PEX but I didn't think pex can turn 90 degree in a tight space. You can see the hot water pex line on the picture

    Thanks

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    Last edited by jerome7; 05-06-2013 at 11:19 AM.

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