PRESSURE DROP FOR SMALL PEX TUBING AT 100 F › Take the total heat load (BTUH) for the area that the loop is covering and divide it by 501. › Divide the result with the Delta-T to find GPM for the loop. › Find the closest flow for the loop in the left GPM column of the chart. › Move to the right to the correct pipe size intersecting. PEX tubing sizes are denoted by CTS (copper tubing size), not OD (Outside Diameter) or ID (Inside Diameter). OD of PEX, copper and CPVC pipe with the same size (CTS) is the same. This is why push fittings can be used with all of these pipes. For this reason you need to be careful when replacing a copper or PE tube with a PEX tube. Often when replacing a copper or PE tube with a PEX tube it is necessary to use PEX that is one size larger than the tube it is replacing. So if you are replacing a 3/4″ copper tube with PEX, you should consider using 1″ size PEX tube for the replacement.
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How to get more water 'pressure' or how to improve water flow rate (gpm or lpm).
This article series explains how to improve water pressure or flow rate and how to improve the total quantity of hot water available from your water heating system.
Page top sketch illustrating the effects of changes in pipe diameter, courtesy of Carson Dunlop Associates, a Toronto home inspection, education & report writing tool firm.
We also provide an ARTICLE INDEX for this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.
Install Larger Diameter Water Supply Piping to Improve Hot Water Pressure & Flow
As we discussed at WATER PIPE CLOG REPAIR, and as we illustrate with Carson Dunlop Associates' sketch shown here, installing larger diameter water supply piping makes a large difference in the water flow rate.
In fact you can improve hot water flow in a building by replacing only part of the supply piping - perhaps that portion which is easily accessible. Installing larger water supply piping feeding the water heater may alone improve the hot water pressure and flow in the building.
[Click to enlarge any image]
Watch out: if your hot water is provided by a tankless coil, increasing water pipe diameter may not be of much use, and it could make matters worse!
A tankless coil (and also an instantaneous water heater) is normally rated by its manufacturer as capable of increasing water temperature to a desired level only if water flow through the coil is limited to a specific rate, perhaps 5 gpm. Flowing water through the tankless coil or instantaneous water heater too fast will mean that the water temperature may be too low at the fixture.
In sum, larger diameter piping increases water pressure and flow. It does not increase the total volume of hot water that is available from a water heater. This improvement may be of most value where water pressure is poor and where water piping has previously become clogged by rust or mineral deposits.
You may regain some of this loss by insulating hot water supply piping or by setting water heater or boiler temperatures higher as well as by an adjustment at
the HOT WATER MIXING VALVE.
Impact of Changing Pipe Diameter on Water Flow Rate
Question: how much water pressure will we lose if we replace copper pipe with PEX of the same nominal size
I have municipal water and a combination furnace. The bathroom shower has separate hot and cold faucets and a diverter from tub spout to shower head.
Recently I noticed that I was using less and less cold water to moderate the hot but only in the shower. The hot in the bathroom sink was still scalding so I knew it wasn't the thermostatic control valve at the furnace.
The only thing I could think it could be was the shower control unit. My thought was that even though the cold was off there was still some cold water somehow mixing with the hot. It had got to the point where you could comfortably take a shower just in hot water while the hot in the sink would scald my hand after a second.
The only logical explanation I could come up with was a failing control as suggested above.
So I have cut out the old unit and replaced it with a Glacier Bay (Home Depot) similar unit. I also replaced the cut out copper with pex and used shark bite fittings to complete the job.
Well, the hot water problem has gone but now I have lower pressure from the shower. I haven't changed the shower head itself, just a few feet of copper to pex, shark bites instead of soldered unions and the fitting itself. I can't say if the tub spout has also been negatively affected.
Do shark bites or pex piping reduce flow ?
Could the new fitting reduce flow, after all, it's a cheapo from Home depot ?
If the water is too hot, should I adjust the thermostatic control at the furnace so I can turn the hot water up in the shower and so increase the volume at the shower head ? That said, it was higher pressure in the old unit so where has that pressure gone ?
Reply:
Shark Bites won't make a notable difference in flow rate; they very slightly crimp the tubing. But as we'll discuss, the smaller ID of PEX tubing may constrict water flow up to ytour shower head.
If the internal diameter of the Pex piping were as large or larger than the piping that you removed and I would not expect it to make a difference in the flow rate. But of course we know PEX has a smaller ID than copper of the same nominal size.
Generally, before ripping out the PEX to go to the next larger size you may want to be sure other easier obvious fixes have been done.
Have you checked the shower head itself? Often mineral scale or debris clog the shower head; cleaning that may be enough.
Reader follow-up:
2020/01/02 Will said:
I have not, it didn't really make sense to me that when changing the fitting the shower would lose pressure because of a part I didn't change.
I'll put a new one on tonight and report back :-)
Also, PEX 1/2' seems to maybe have a slightly smaller internal diameter than copper 1/2' due to the thickness of the pipe wall.
Moderator reply: Calculating the reduction in pipe cross-sectional area when changing from Copper to PEX = Reduction in Water Flow Rate
Will
Thank you for asking a great question: how much difference to water flow does changing from Copper to PEX make if the nominal pipe sizes remain the same.
At WATER PIPE CLOG REPAIR we explain that as illustrated with Carson Dunlop Associates' sketch, installing larger diameter water supply piping makes a big difference in the water flow rate.
I am (sorry to say) far too familiar with the effects on water flow rate (popularly called 'water pressure') of reductions in the diameter of a supply pipe, thanks to a lazy local Poughkeepsie plumber who used 1/2' instead of 3/4' ID PEX on a job.
That reduction in diameter when changing to PEX or when including ANY PEX in the piping run can show up as a complaint of a weaker shower flow just as you’ve suggested.
In general, the greater the percentage of smaller diameter piping in a water system the greater the reduction in flow rate, all other factors (such as pressure, total piping length, number of elbows, valves, etc. ) remaining the same).
The ID of copper pipes is ROUGHLY 1/8 less than the OD. But the actual copper piping inside diameter (ID) number varies as across types L and M the OD stays the same.
'Type K tube has thicker walls than Type L tube, and Type L walls are thicker than Type M, for any given diameter. All inside diameters depend on tube size and wall thickness.' - copper.org cited below
- Nominal 1/2” K Copper: OD: 0.625” ID: 0.527” Wall: 0.49” Cross-Sectional Area: 0.218”
- Nominal 3/4” K Copper: OD: 0.875” ID: 0.745” Wall: 0.65” Cross-Sectional Area: 0.436”
- Nominal 1/2” PEX: OD: 0.625” (same as copper), ID: 0.485” (0.005” smaller than copper), Wall: 0.70” Cross-sectional area: (pi r squared = area of a circle & r= 1/2 diameter): (3.1416 x 0.2425 (squared)) = 0.185”
- Nominal 3/4' PEX: OD: 0.875” (same as copper), ID: 0.681” (0.064” smaller than copper), Wall: 0.097” Cross-sectional area: .364”
Percent decrease in cross sectional area going from copper to PEX
Percent decrease in cross sectional area going from copper to PEX is about the same as the percent reduction in water flow through the piping, if all other factors are kept equal:
- 1/2” PEX = 15% less cross-sectional area & flow rate than 1/2” copper [ 1 - (0.185 / 0.218) x 100 ]
- 3/4” PEX = 16% less cross-sectional area & flow rate than 3/4” copper [ 1 - (0.364 / 0.436) x 100 ]
Pressure Drop When Using a Smaller Pipe Size
Pexuniverse gives nominal pressure drosp in psi per 100 ft. of tubing length for several flow rates from which we excerpt below.
At Flow Rate of 1 GPM
- 1/2” PEX has a pressure drop of 1.70 gpm per 100 ft. of run
- 3/4” PEX has a pressure drop of 0.34 gpm per 100 ft. of run.
This is very significant as it illustrates that a reduction of 1/4' in the ID of PEX going from 3/4' down to 1/2' tubing will give a net change in pressure drop of (1.70 - 0.34) or 1.36 gpm over a 100 foot run (all else unchanged).
That's a 400% greater pressure drop per 100 ft. of run when going to one nominal smaller pipe diameter smaller. The numbers for copper piping pressure drop as diameter changes will be similar.
Ilustration courtesy of Carson Dunlop Associates discussed further at CLOGGED SUPPLY PIPES, REPAIR
Research on Plumbing Pipe Size vs Flow Rates
- ASTM-F876 “Crosslinked Polyethylene (PEX) Tubing
- COPPER TUBE HANDBOOK [PDF] at inspectapedia.com Copper Development Association, Inc., 7918 Jones Branch Dr., Suite 300, McLean VA 22102 USA Website: https://www.copper.org/ Original source: https://www.copper.org/publications/pub_list/pdf/copper_tube_handbook.pdf
- PEX TUBING TECHNICAL SPECIFICATIONS [PDF] PEX Universe.com (Sales of PEX tubing) Tel: 800-818-3201 original source: https://www.pexuniverse.com/pex-tubing-technical-specs
- SharkBite Plumbing Solutions, SharkBite USA 2300 Defoor Hills Rd. NW Atlanta, GA 30318 USA Tel: 1-877-700-4242
SharkBite Canada 74 Alex Avenue Vaughan, Ontario, L4L 5X1 Canada, tel: 1-888-820-0120 retrieved 2020/01/19 original source: https://www.sharkbite.com/
SHARKBITE INSTALLATION GUIDE [PDF] (2018) Reliance Worldwide Corporation 2300 Defoor Hills Rd NW, Atlanta, GA 30318 Phone: 1-877-700-4242 Fax: 1-877-700-4280 rwc.com Reliance Worldwide Corporation (Canada) Inc. 74 Alex Avenue Vaughan, Ontario, L4L 5X1 Phone: 1-888-820-0120 Sales Inquiries: canadasales@rwc.com Orders: canadaorders@rwc.com retrieved 2019/08/13 original source: https://www.sharkbite.com/sites/g/files/rgohfh321/files/2018-05/SharkBite_Installation_Instructions_2018_WEB.pdf
Reader Comments & Q&A
On 2020-05-18 by Gowtham
I need a fogging calculations . With 14 por 12 fogging nozzels 80 littes of water has to be consumed for 9 hours.which motor and nozzels are adviced .
Presently i used half hp submercible pump 6mm numatic pipes and 0.2mm 7 nozels.its consuming 80 ltrs of water by 6.30 hrs.
I have done many experiments on this .now i want to change to 1/4 hp motor .i thought this may increase more time.
Can someone suggest me.
Iam doing it for disinfection tunnel.
Disinfection liquid is costly so iam trying it do a fog .
On 2020-02-10 - by (mod) -
Will
Thanks for the follow-up as that will help other readers;
On 2020-02-10 by Will
OK, so I finally got around to at least changing the shower head for the cheap plastic one that came with the fitting. Before putting it on I drilled out the restrictor and it's made a huge improvement. So perhaps the PEX isn't an issue after all :-)
On 2020-01-07 - by (mod) -
If you take a look at the explanation above on this page you'll see the effect of replacing part of water piping with a larger diameter.
Let's take it step by step doing the easy things first as we've been discussing.
On 2020-01-07 by Will
You said 'About going to 3/4' copper throughout, that gives much greater delivery rate of water but may not be necessary; As Carson Dunlop's sketch on this argues, often replacing just the accessible part of supply piping with larger diameter makes a big difference'
Does that statement suggest that if I take the 1/2' hot water supply from the furnace and a couple of feet away from that connection to the furnace I convert the 1/2' to 3/4' I will see a noticeable difference if I keep that 3/4' all the way to the shower fitting where it has to go back to 1/2' to connect to the shower fitting ? Doesn't the fact that the supply from the furnace starts out as 1/2' cause a bottleneck that isn't corrected when the diameter increases further down the line then decreases again at the fitting.....or doesn't water pressure/flow work that way ?
Meantime, I'll remove the restrictor, hadn't even occurred to me. Thanks
On 2020-01-06 - by (mod) -
Will
You can also stay with PEX but go to the next larger size, with proper adapters to connect it to your existing piping.
About the shower head: it is probably a low-flow shower head as most are currently; at low water supply pressure systems where going to a low-flow shower head gives unacceptable water flow for bathers, I either pull out the restrictor in the shower head (usually it's right in the screw-on fitting) or if necesssary I drill out the opening into the shower head at its connector.
About going to 3/4' copper throughout, that gives much greater delivery rate of water but may not be necessary; As Carson Dunlop's sketch on this argues, often replacing just the accessible part of supply piping with larger diameter makes a big difference. I'd go step by step.
On 2020-01-06 by Will
And, furthermore, would you recommend swapping out all hot and cold water lines for 3/4' copper ? I might have a problem doing that with the hot as it comes from a combi furnace and I believe the only hot outlet is 1/2' so making it 3/4' a foot from the 1/2' outlet and then maintain 3/4' all the way to the faucets/shower would be a waste of time, correct ?
In any event, the shower fitting itself is 1/2' so wouldn't that create it's own bottleneck anyway ?
Thank you for the assistance and the subsequent comments on the theory that the PEX is causing a lower pressure at the shower head. I have now since swapped out the shower head for a brand new head, albeit low budget, from Home depot. If anything the pressure is even lower than before. I have to assume that the PEX is causing a reduction in volume which manifests itself as low pressure at the shower head.....I guess I'm getting some soldering practice in the near future. Low shower pressure is a pet peeve of mine.
...
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