New water heater doesn't have the capacity of old one (but it should)

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Djarchow

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We had our 19-year-old 50 gallon Rheem powervent water heater replaced this year as the old one finally rusted through. We had it replaced by a new 50 gallon Rheem powervent classic water heater. The new one seems to have noticeably less hot water capacity than the old one. With the old one we could always get through a shower, even a relatively long one, with hot water. With the new one it seems even after 10 minutes we have to start cranking up the temp in the shower to keep it hot.

I have measured the temperature of the hot water coming out of the new one and it is 120 deg. just like the old one. Looking at the specs for the old one and the new one the BTU/hr ratings are similar (40-42k) and the recovery in GPH at 90 deg rise are also similar at 40-42 gallons. The first hour rating on the old one was a couple gallons higher but not significant. All the inputs to the new water heater including gas and water lines are the same as the old one.

Any thoughts on what might be causing the new one to run out of hot water sooner than the old one?

Thanks in advance for any advice!
 

John Gayewski

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Is your shower cartridge in good shape?

If you know it's not the cartridge then take it up five degrees or so. There's not much you can do to change anything. I suppose you could try pulling the dip tube, but I think there would be a more dramatic difference if there was a problem with it.
 

Jeff H Young

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Is your shower cartridge in good shape?

If you know it's not the cartridge then take it up five degrees or so. There's not much you can do to change anything. I suppose you could try pulling the dip tube, but I think there would be a more dramatic difference if there was a problem with it.
agree on cartridge or ballancing spool but the water heater swap shouldnt have caused cartridge to act up but kinda doubtful the diptube is cracked or something as well I dont see how else the capacity of hot water would be less
 

John Gayewski

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Any time the piping is disturbed and things get stirred up a cartridge can get stuck. Or if it's the same age as the water heater is just a coincidence that the seal is mixing between chambers from age.
 

Djarchow

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Thanks for all the replies. We are seeing the same problem with all the showers in the house. When I showered last night, I decided to keep an eye on the clock. The temperature stayed consistent for about 6 minutes with a 2.5 gpm shower head but by 8 minutes it had noticeably dropped. If the shower head rating is correct, I would have used about 25 gallons out of the 50 including the time I let it run to warm up.

I will check how much gas is being used on the meter when a shower is happening. We are in the middle of a snowstorm with 40mph winds so will probably check tomorrow. Thanks again everyone.
 
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