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Observation: the flame on water heaters will sometimes be yellow on start up (or more likely a few seconds after what appears to be a good start up) when cold because of condensation falling into the burner pan. Once the water in the tank reaches sufficient temperature, the condensation stops and the flame should turn blue again. Unfortunately, this is NOT pointed out in most manuals. That puts one in the uncomfortable position of watching the yellow flame for some minutes until the tank warms...
When you say you are losing hot water after 15 minutes of showering, what sort of flowrate are you talking about? Is this a single head shower with a modern showerhead (~2.2-2.5 gpm operating flow), or is it a multi-head shower or old 5 to 9 gpm showerhead?
All that said, Jim's comment about the sizing of the gas lines is where I would start looking based on your description. I suppose it is also possible that the dip tube is missing or broken.
Yeah, modern showerhead, 2.2-2.5 GPM. Old 50 gallon water heater this one replaced was in the process of dying, but still lasted for at least a 30 minute shower before losing most/all hot water.Originally Posted by Runs with bison
I called Rheem and they're sending out one of their guys next week who has experience with these units. Will let you know what I hear, but the gas pressure issue sounds most plausible at this point...the guy who installed it certainly never measured it.
I agree. A manometer needs to be connected to the unit while its firing.
So, as an update, had Rheem send out one of their tech's for warranty service. They said the flame looked fine and refused to do any gas pressure tests.
Also, they did a drop test and said the temperature drop was right on "for a 29 gallon tank."
With that I got pretty upset given all of the "outperforms 50 gallon tank" claims in their promotional literature and press releases (one press release falsely stating that "Once the Rheem XR90 has been depleted of its available hot water, the unit can be ready with 90 gallons of available hot water in only 29 minutes.). I said the heater doesn't outperform my old 50 gallon (which gave me ~ 30 minutes of hot water in the shower). The tech put me on the phone with a Rheem rep, who stated that the XR90 will only match a standard 29 gallon tank for a continuous draw of hot water.
He claimed the tank only outperforms the 50 gallon tanks on recovery rates (e.g., after you stop pulling hot water out of the tank).
He concluded that a 15-20 minute shower using a 2.2-2.5 gpm shower head should be about all you get out of this tank. (then you have to wait another 30 minutes for the tank to heat up).
Now I'm stuck trying to decide whether to raise hell and get a lower efficiency tank, or stick this one out and crank up the temp on the tank...
But either way, Hackney Plumbing's calculations earlier in this thread of this tank supporting a 52 minute shower are way off, and should not be relied upon by those considering this tank in the future (assume 15 minutes).
My calculations are based off the manufacturers specs. If the specs are off then for sure my calculation will be.
The unit with the much higher BTU rating will out perform the standard burner and the same size tank.......thats a fact.
No one can simply start telling you maximum shower times without knowing how hot you like your shower,how much your flowing and the temp of the cold water. Without those its a guess.
My wife and I can take back to back showers in the summer 15 minutes each and running about 4 gallons a minute....with a 50 electric. That works out to about an hour at 2 galllons a minute if we had low flow heads installed.
Crank the heater up as high as it will go and install a tempering valve....you'll have enough hot water.
Last edited by Hackney plumbing; 04-13-2012 at 01:33 PM.
In other words, Rheem doesn't really stand behind their product. They make exaggerated advertising claims. The likely problem is that small tanks are going to have too much mixing with incoming water and therefore cool off perhaps twice as rapidly as a 50 gallon tank. Who cares how fast they can recover if they get cold before the shower is over?
I'll stick with 50 gallon tanks. Reducing tank size doesn't accomplish much efficiency wise anyway, because much of the loss is in the uninsulated combustion chamber, flue wall, and nozzle projections. So if one is going to have a tank at all, it might as well be a 50 gallon or take the leap to tankless.
We sometimes have all three showers running (1.5-1.6 gpm shower heads) and never come anywhere close to running out of hot water. The only time we've come up short is during whirlpool tub fills with 125 F set point on the water heater in cold weather. And even that recovered in 15 minutes. Raising set point a few degrees has eliminated that issue as well.
Seems kind of stupid or lazy for the manufacturer's rep to come out and then not measure the gas pressure. Eyeballing the flame isn't likely to show if the duty is only 2/3 of normal or so.
I agree. It should have been checked. If the input is low then the BTU rating goes out the window.
Just to cap off this thread, Rheem finally agreed to replace the 29 gallon tank with a 50 gallon tank at their cost (after more push back from me than it should have taken, but I understand they're trying to minimize costs).
I ended up going with Rheem's 50 gallon powered damper model that only lowers the efficiency rating (from the XR90's 0.7) to 0.68 (the damper closes after the flame extinguishes and helps further insulate the combustion chamber, which as you noted above RWB is a major source of heat loss).
I've been extremely happy with this unit, and am back to getting a seemingly endless supply of hot water.
-Dan
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