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Summary: Low water flow to a shower head can be caused by a low-flow rough-in valve/cartridge
Every hotel I’ve ever been to has a shower head that blasts me with more water than I could ever need. But the one in my house sends out just a trickle by comparison. I know there is a federal regulation that requires shower heads to produce no more than 2.5 Gallons Per Minute (GPM) at 80 PSI but I assume hotels are also bound by those rules. I’ve been baffled by this problem and for years I didn’t know how to fix it. Now I’ve finally figured it out.
I measured the water flow rate from my shower head and got 1.0 GPM, but I can get nearly 10 GPM from the utility sink in my basement. Even when the shower head and tub spout are removed the water flow is 1.4 GPM or less from the bare pipe, so I know it’s not the fault of the restrictor in the shower head. I have 40 PSI municipal water and copper pipes throughout the house. Here are the measurements I took:
Shower head: 1.0 GPM
Bathtub spout: 1.4 GPM
Shower pipe w/o shower head attached: 1.1 GPM
Tub spout pipe w/o spout attached: 1.4 GPM
Toilet in the same bathroom: 3.9 GPM
Utility sink in the basement: 9.9 GPM
Since I have great pressure elsewhere in the house, next I checked if there might be something gummed up in the shower valve blocking the water flow. I unscrewed the hot water handle and removed the cartridge, but it was nice and clean and there didn’t seem to be any blockage in the pipe, either. I turned the water supply to flush out any unseen blockage that might be in there and just to see how much water would come out. Lots! But when I put the cartridge back in I got the same poor water flow. I did notice the cartridge lets water in through two tiny little holes and thus makes a great bottleneck. It seems like it is designed to reduce water pressure by about 80-90%. It is essentially a low-flow shower valve and no matter what shower head I use it will provide poor water flow.
I did some googling and called some plumbing supply stores but as far as I can tell no one has ever heard of a low flow shower valve or low flow cartridge. Everyone suggests checking for a partially closed shut-off valve in the line, gunk clogging up the valve, a restrictor in the shower head, corrosion inside galvanized pipes, or low water pressure to the entire house. I don’t have any of those problems.
I asked some plumbing supply stores and a plumber, but there doesn’t seem to be a different cartridge I could buy that would increase the water flow. This cartridge doesn’t have a part number or brand name anywhere on it but it looks like an imitation Moen cartridge. After I tried to drill it out and caused a leak, I replaced it with an Ace hardware part called “Faucet Stem Moen Style 6S-1H/C Hot/Cold stem.” It’s a replacement for a Moen 1224 stem but it looks like my shower never had a genuine Moen part.
I went to Home Depot to check out rough-in valves there, but there is no information provided about water flow rate. On American Standard’s website, however, there are some spec sheets for their rough-in valves that give water flow rates. My solution was to replace the rough-in valve with an American Standard part and now my water flow rate is much improved.
I have heard that the 2.5GPM government regulation caused some manufacturers to overcompensate and produce super-low-flow components that are way below 2.5GPM just to be on the safe side. But as far as I know, that regulation applied to shower heads and kitchen/bathroom faucets, not to the shower valves themselves. It seems that my shower valve was made with stems/cartridges that are also used for bathroom sink faucets, and those are limited to 2.2 GPM at 80PSI by law. It just seems like a bad design to carry those parts over to a shower/tub valve. It used to take half an hour to fill the tub, which is really annoying and benefits no one.