Choosing the right pipe size for Dornbracht shower fixtures.

[johnfrwhipple]

We have started a fantastic shower renovation here in Yaletwon, Vancouver. The shower will be trimmed out with some great lights and an amazing Dornbracht package.

We shut the water off to the condo yesterday and removed as much of the condo's old Poly B as we could and installed some new 3/4" supply lines for the shower - both hot and cold.

My client is concerned that the 3/4" pex pipe will not produce the same volume as say 3/4" copper. The condo has it's own isolation valves so switching at this point is not the end of the world but I have never seen a shower valve roughed in with 1" pex before - that said I have never installed so many German fixtures in one shower before.

Is there a huge difference in flow rate? I'm sure the valves on the Dornbracht fixtures can not handle this much water as not many homes have this same set up as a condo. I have email Dornbracht and look into this further before proceeding with any more work.

A sneak peak at our project...


http://www.dornbracht.com/en/index.htm?nav=1051&cid=5

[jimbo]

I don't have a spec sheet handy, but I would guess that 3/4" PEX might be suitable for 6 to 8 gallons per minute. If you go higher, you may exceed acceptable velocity range, and may experience excess pressure drop. So I would start by figuring out the GPM draw of whatever is being put in. As you are in Canada, you may not get the visit from the algore about that water usage, but he does extend his influence world wide!

[johnfrwhipple]

6 gallon per minute GPM [US, liquid] or 22.712 470 704 liter per minute

8 gallon per minute GPM [US, liquid] or 30.283 294 272 liter per minute

A personal volume test in my home here in North Vancouver with a 3/4" water line at 104 PSI passing through 10' of 3/4" pex pipe with 2 couplings and 2 1/4 turn 3/4" shut off's produced 1.15 litres per second or

18.24 gallon per minute GPM [US, liquid] or 69.045 910 94 liter per minute

I'm waiting on feed back from Dornbracht.

Who out there has set up a similar test or measured results from their personal project?

Any insight or suggestions are welcome.

[jimbo]

Geez....what are you running at 104 PSI? And what is the water velocity in Feet per second? You can make water flow, but excessive velocity will wear fittings, pipes, and valve components!

[nukeman]

18.24 GPM = 2.446 ft^3/min

Nominal ID for 3/4" PEX = 0.671 in

Flow area = pi*D^2/4 = 0.3536 in^2 = 0.002456 ft^2

Velocity = 2.446/0.002456 = 995.9 ft/min = 16.6 ft/s

[jadnashua]

I think you are exceeding the velocity to get that volume. This can lead to premature wear. Normally, 80psi is the max recommended in a house, and most people live quite well with less.

[johnfrwhipple]

The pressure of the finished system will be 70 PSI aprox. My home has a PRV and the day to day pressure is set to 70 PSI. The 104 PSI I reached before my PRV and feeds my front yard sprinkler feed (I tied in here to gain the maximum amount of water for my Quick Drain USA channel drain test.

Nuke man that is great!

[nukeman]

Flow at 70psi can be approximated by taking the ratio of the squareroot of the pressures. Like this:

Say you are getting 18.24 GPM at 104 psi.

At 70 psi, the flow should be [sqrt(70)/sqrt(104)]*18.24 = 15.96 GPM (13.6 ft/s in 3/4" PEX)

Double the pressure gets 1.414 times the flow. To double the flow, you need 4x the pressure.

[jimbo]

http://www.toolbase.org/PDF/DesignGu...esignguide.pdf see page 80

You haven't told us the GPM requirements of your set up, but the design guide link shows that for 3/4 pex, you might get away with 6 or 8 GPM, but it gets very dicey above that.

[johnfrwhipple]

We have piped the shower with 1" pex to insure the maximum amount of water gets to the shower. We have 40 PSI on the job site the result of a drop in pressure going 12 floors up (pressure in the mechanical room of the building is 70 PSI).

So if you have 40 PSI and two 3/4" supplies with a few random fittings and you run new 1" pex from that about 12' away again with random fittings and such you can fill a 77 Litre garbage can in 25 seconds flat. OMG is that fast!

This is a massive amount of water and exceeds my home testing and the capacity of the drain. We have installed to globe valves so we can restrict water flow and tame back this shower system to work with our new 2" Channel Drain from Quick Drain USA.

I'm very curious to measure the output with the fixtures installed and their design water restrictors working.

I set the shower pan last night. The shower pan is 60" x 28" and grades from the East to the West at a quarter inch per foot.

I have pictures but no camera cord once again. I have to find a better spot for that cord...

[johnfrwhipple]

Shower (based on the total flow rate through showerheads and body sprays)


Flow rate:

5.7 gpm or less 1 1/2" P-Trap
Greater than 5.7 gpm to 12.3 gpm 2" P-Trap
Greater than 12.3 gpm to 25.8 gpm 3" P-Trap
Greater than 25.8 gpm to 55.6 gpm 4" P-Trap

This should help you select the proper drain for your next shower package. I have noticed slower drainage rates for the tile insert point drains and linear drains so if your close to one of these limits it would be wise to select a drain with a grill or the next largest P-Trap size.

JW

[EuroPlumber]

Hi John,

Good looking shower but I can't believe you are working on piping with the walls finished. In my experience and research PEX is equivalent to copper in regard to flow rate. There are some good points made above about flow rates and how they can errode the copper PEX fittings if the flow rate is too high. You should never exceed 7.5gpm on a 1/2" copper system for this reason, plus noise becomes a factor. For 3/4" Copper or PEX you should hold the flow rate under 15gpm for the same reasons. PEX fittings are copper and can errode with too high a flow rate, but they have been demonized by many plumbers and copper mfg industries because you need less copper and less precision to install PEX. Yes, the fittings are inserted into the interior of the PEX pipe and have a slightly smaller inside diameter than copper fittings, but the transition from PEX to it's copper fitting is pretty smooth and errosion should not be a factor unless the flow rate goes too high. Right now, I am wondering how many plumbers will read this and say that copper is just plain better. I would agree that it can be in many ways better, but it isn't always the best. If you get a plumber who is in a hurry to make money and run, he won't bother to ream the pipe which can cause erosion faster than that nasty PEX fitting they don't like. Anyway enough rant on that. Figure the PEX the same as copper. Make some nice radius bends with it and you will eliminate some fittings all together.

Call or email me if you need anything from Dornbracht. I am Phil the Technical Service Manager for the American market.

Cheers!

[EuroPlumber]

My signature line is wrong in the above. I have updated it to the Dornbracht contact.

[EuroPlumber]

Yet it still shows Hansgrohe. I will try again.

[johnfrwhipple]

My signature line is wrong in the above. I have updated it to the Dornbracht contact.

Isn't your timing perfect. I would love to chat with you about a current build I'm working on. We are using mostly Dornbracht fixtures with some Gessi Vapourizors or misters in the ceiling. Do you recommend a certain pipe size for these misters?

I'm also in need of some Euro to North American adapters.

Could you call me tomorrow? 604 506 6792

Thanks!

JW