I recently replumbed our house with ¾” copper and pex running to the second floor bathroom. It is a small house with 1.5 bathrooms, kitchen, washing machine and utility sink. We plan to eventually add another full bathroom. We replaced he ancient galvanized pipes (pressure wasn’t great and water quality was terrible) and everything was fine but recently my wife was in the shower and I happened to flush the toilet…and the pressure dropped. I was shocked… where did I go wrong?

Details: Except for the hose bibs and cold water in the kitchen. Everything runs through a water softener. From the softener runs the cold water line, feeding the washing machine and utility sink, ½ bathroom, and a pex connection to the second floor bathroom. The line heads to the water heater, which then feeds the same fixtures on the way back.

Did the whole house get replumbed, or just the lines to the upstairs. Put your softener in bypass mode and see if you still get the pressure drop.

Well or Municipal water supply? Did you remove and check the shower head for debris? Do you know the flow rate thru your softener? Can you switch it to by-pass and see if that makes any difference?

KC- your post beat mine by 10 seconds. You type fast. I could type faster if I didn't have to stop and think



Edited 1 times.

ID of 3/4 Cu tube does NOT = ID of 3/4 PEX

ID of PEX is approx. one size smaller (equivalent) due to wall thickness and fitting restriction(s)


Sorry for the unwelcome news


I hope that you have another issue as this will require a 'rework' if applicable.

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

There are MANY possibilities and each requires a different test and cure. Do you have a pressure regulation valve in the water line?

Thanks for the responses. I did replumb the whole house. The pex lines to the second floor are ½” home runs to each fixture off of the ¾” copper in the basement. It is a municipal supply with a PRV set to about 60 at last check. It is a Whirlpool softener with a minimum flow rate of 3gpm. (It also says intermittent flow is 15 at 30psi)



Edited 1 times.

1/2 PEX is slightly more ID than 3/8 Copper

NOMINAL SIZING

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Ok - Everyone I spoke with (and advice from this site) was that homeruns of 1/2" pex off of 3/4" copper would be fine. You are saying that I should have run 3/4" pex home runs?

Also, if they are home runs - why does the size of the home run cause the shower to drop in pressure? It seems like the same problem would occur with bigger pex since they are both pulling from the same 3/4" copper main.

Your PRV is most likely clogged with debris and is the equivalent of one lane on a 12 lane highway. When the demand is small, it allows enough water by, when you need more, it just can't pass in time, and the highest/furthest fixture looses out.

Interesting thought - why do you think that? It is pain to get it off but I have isolating valves and should be able to clean it. Is there a way to test it without taking everything apart?

You already determined that the pressure dropped significantly when the toilet was flushed, and this is due to a volume restriction. Your shower is restricted to 2.5 gallons per minute at the shower head, but the toilet doesn't have a restriction other than the flow rate due to pipe size. If you had sufficient volume prior to replumbing with galvanized and the pipes are clear and new now, then your problem is a flow restriction. When the demand for water is higher than the flow permits, there isn't enough volume to feed both fixtures adequately, so the pressure drops off until the toilet is full and the shower gets all the pressure and volume again. Some Prv can be cleaned and returned to service; if it is new, clean it, if not, I would replace. Next time that you need to replace it, be sure to install unions so that the water can be shut off and the pipe separated at the unions.