Hot water line size needed for multiple head shower

[MrJOAT]

I’m planning a multi-head shower (6 body spray, rain tile, and regular shower head). Will have an 80 gal/max – 60 gal/min whirlpool too. I currently have ¾ pex hot and cold supply lines available. I have a recirc return line there too. The shower is on the second floor and HWH is in the basement. There is no plan to use the shower and tub at the same time

There’s a 40 gal HWH used as a storage tank off the Geo de-super heater. This feeds the 55 gal AO Smith electric HWH with ¾ copper out – ties to a manifold then ¾ pex to the shower. About a 40’ run

The de-super heater is providing hot water to the 40 gal tank during the heating and cooling season. This is about 8 months out of the year. The holding tank is not currently wired, but could be to provide additional hot water with the 40 gal and 55 gal in a series.

Questions:

With the body sprays and rain tile all turned on, will I be pushing the hot water supply (3/4 line capacity/flow) too much? Could be 16 – 18 gpm on the high side? The exact fixtures have not been selected. Doubt we would typically run all at once, but would like the option.

1. If I need a 1” hot water supply line, will the ¾ outlet from the top of the HWH be a bottleneck?
   
   
2. For more hot water, could I add an additional ¾” line from the tank instead of running a 1” line? (there’s a manifold I could tie into). Does this fall into the same potential concern of the ¾ hot off the top of the tank.

This remodel is a full demo. I’ll be in the floor to move drain lines and can open walls/ceilings to run supply lines as necessary. I may have a 2x6 wet wall for the valves/piping/venting.

Many Thanks!

Matt

 

[Jadnashua]

The maximum recommended gpm with 3/4" pex is 12gpm, and, in a 100' length, at that flow rate, you'd lose over 25# of pressure from friction losses.

You need to add up the gpm of each of the items you want to have on at any one time then you can make an assessment of whether it would work out for you. This article may help...

https://www.pexuniverse.com/pex-tubing-technical-specs

And, yes, the inlet/outlet to the WH will be an issue. FWIW, the Copper Institute calls for a maximum velocity in copper piping of 5fps with hot water, which, on 3/4" copper equals only 8gpm. Yes, you can exceed that, but there are ramifications: noise, pressure loss, eroding of the actual pipes. Pex allows a higher velocity, and therefore volume, but still has frictional losses...not as many as with copper piping unless you plumbed it similarly by using lots of fittings to make it look neat, verses just bending the tubing when needing to go around a corner. Plus, the ID of pex is a factor - it's measurably smaller than on copper.

 

[Sponsor]

 

[Mr.JOAT]

The maximum recommended gpm with 3/4" pex is 12gpm, and, in a 100' length, at that flow rate, you'd lose over 25# of pressure from friction losses.

You need to add up the gpm of each of the items you want to have on at any one time then you can make an assessment of whether it would work out for you. This article may help...

https://www.pexuniverse.com/pex-tubing-technical-specs

And, yes, the inlet/outlet to the WH will be an issue. FWIW, the Copper Institute calls for a maximum velocity in copper piping of 5fps with hot water, which, on 3/4" copper equals only 8gpm. Yes, you can exceed that, but there are ramifications: noise, pressure loss, eroding of the actual pipes. Pex allows a higher velocity, and therefore volume, but still has frictional losses...not as many as with copper piping unless you plumbed it similarly by using lots of fittings to make it look neat, verses just bending the tubing when needing to go around a corner. Plus, the ID of pex is a factor - it's measurably smaller than on copper.

****
Jim, thanks for your reply nearly a year ago! Shortly after I asked the questions I had some military travel and never got back to my bathroom project or this forum. I posted new thread a couple weeks ago asking the same questions and several more as I could not find this original post from last year.
I have decided to run 1" pex lines to the shower. I'm just now trying to plan/spec this long overdue project.
V/R
Matt

 

[Jadnashua]

Let us know how it all works out.

 

[Mr.JOAT]

Somehow I decided to add steam. I'm actually stuck at the framing part/design due to need for a sloped ceiling??? Many say you need a sloped ceiling yet there are just as many that say in a residential application, a slope isn't really necessary let alone required.

For plumbing related, I continue to review other threads for ideas/product info. My current challenge deciding if separate volume controls are better or if using a multifunction valve or two is better. Leaning towards separate valves for each function.

 

[Jadnashua]

A sloped ceiling helps prevent cold drips from raining down on you! How quickly you'll accumulate them would depend somewhat on how long the thing was running, how well the ceiling was insulated, and how well the steam shower was enclosed. Drops can still fall off because of uneven grout joints.

Check out www.johnbridge.com for help with tiling things. Some will also have some experience with the control valves, but the plumbers here will as well.

I've not really dealt with a steam shower.

Waterproofing the shower becomes a much more rigorous job when you consider steam. Not all waterproofing systems work well enough with high vapor pressure. There are different recommendations for residential and commercial steam showers since a commercial one might run literally 24/7.

 

[Mr.JOAT]

A sloped ceiling helps prevent cold drips from raining down on you! How quickly you'll accumulate them would depend somewhat on how long the thing was running, how well the ceiling was insulated, and how well the steam shower was enclosed. Drops can still fall off because of uneven grout joints.

Check out www.johnbridge.com for help with tiling things. Some will also have some experience with the control valves, but the plumbers here will as well.

I've not really dealt with a steam shower.

Waterproofing the shower becomes a much more rigorous job when you consider steam. Not all waterproofing systems work well enough with high vapor pressure. There are different recommendations for residential and commercial steam showers since a commercial one might run literally 24/7.

I have been to johnbridge and read a ton of info. From what I've gathered there and at some other forums, it's 50/50 on the sloped ceiling. Many residential installer mentioned putting in flat or perhaps it was homeowners (DIY) installs being placed flat with no problems. The grout lines dripping from slopped installs dripping was mentioned numerous time. Typical 20 minute steam sessions was also mentioned as not being longe enough to cause the condensation on the shower ceiling. I'm thinking flat ceiling. Will look better and be easier.

Waterproofing: - looking at the USG product. Has the lowest perm rating.

 

[Jadnashua]

The perm rating becomes more critical the more frequently the steam shower is used and the interval between uses. In most cases of a residential unit, something below 0.75 is often sufficient. In a residential situation things get to dry out in between uses. There's a commercial perm limit for steam showers. Meeting that in a home can be done, but isn't necessary in most cases.

How much condensation you get on the ceiling is both a function of how long it is in operation, but also how well the ceiling is insulated.

 

[Mr.JOAT]

Perm ratings: I have some kerdi left over from a previous shower project. I think it's .75 perm. Several members on the johnbridge site said the USG is easier to work with and has a lower perm rating so I started looking that direction. I haven't looked to see if the USG is picky about modified vs non modified thinsets. As for usage, I wouldn't think the steam shower would get used for more than an hour a day.

Any experience with different steamers??? I'm leaning towards Thermosol.

Insulation: yes, I'll definitely have an opportunity to super insulate the ceiling. I'm building a flat ceiling for the shower that's below a vaulted bathroom ceiling. The flat ceiling I build will line up with the existing lowered ceiling sections (plant shelves as others call them)

 

[Jadnashua]

KerdiDS has a better perm rating, and is what Schluter calls for in a commercial steam shower. In a residential one, either will work along with the USG product. Someone gave me a sample, but I've not used it. You should have a reliable install with either assuming you follow the instructions carefully. While I wouldn't, RedGard has a pretty low perm rating, too. IMHO, though, too easy to not get a consistent coating with liquids.

I've not dealt with steam generators, so can't offer any useful comments. Pay close attention to clearances to the steam outlets relative to the membrane and seals you may use. Actual steam at sea level, will be at least 212-degrees F...the films are not rated above about 180-degrees if my memory serves, so clearance is important.