What is the definition of these common terms used in the gas water heater mfgr specs:

1) Recovery in G.P.H 90 deg rise

2) First Hour Delivery G.P.H. -- What is the temp drop allowed over the first hour...?

Thanks!

Rheem defines recovery as: BTUH input divided by ( 11 X tempriseº)

They also define first hour delivery as: (TankGallon X.0.7) + recovery


This is based on the 70% assumption. Given "average" ground water temp, and a 75% efficiency gas burner, a water heater will deliver 70% of its gallon capacity at a temp between the tstat setpoint and a temp 20º lower than that. This is do to cold mixed in as soon as you start drawing hot water.



If you love water heater stuff, go to Rheem.com They have enough technical bulletins on there to make your eyes glaze over!



Edited 1 times.

1) Recovery in G.P.H 90 deg rise

How many gallons will be heated in one hour at a 90 degree temperature differential. Using 90 degrees instead of the standard 100 degrees gives a better number. It is a nebulous number because the incoming temperature can change, and the temperature of the stored water constantly changes as it becomes heated.

2) First Hour Delivery G.P.H. --

A combination of the storage capacity of a fully heated tank, plus the recovery rate. Once the tank is depleted you have to rely on the recovery rate for your hot water.

Jimmie-o,
Thanks for the response..!

How did you change the message subject line...? I tried to do this once and it ignored my input....

As to your definition: <<This is based on the 70% assumption. Given "average" ground water temp, and a 75% efficiency gas burner,>>

I hope the numbers in the tables published by the WH mfgs are based on testing and not so many assumptions. I was using the 90 deg rise spec to calculate the BTU/H actually put into the water in the tank.

I am looking for a replacement WH for my combo hot water and water furnace system. 9 years ago I bought a Rheem Vanguard (Grainger retail) gas WH with 75KBTU input. It was overkill, but cheap and a high efficiency tank (near 80% burner efficiency -- had three flue-tubes thru the tank). Now it has sprung a leak and nothing like it available. So trying to calculate what I really need in BTU.

Seems once you go for more than 40K BTU/H, you get into spendy territory, and I fear also lower longevity as heat input goes up.....

I will take a look at the rheem docs... hope they are easier to search than the messages on this board....

They do engineering calculations. What I mean by assumption is that you can't put out one number that takes into account the total possible variations in groundwater temp, therm multiplier on the gas, etc. etc.

Down-sizing to a 50 gallon WH with only 40K BTU input may be asking for problems...like running out of HW.

I was on a job just today in a rental property that SXXXX had recently installed a new 50 gallon model with 40K input, the HW temperature was cranked up to past the "B" setting, I found this out after testing the water temperature when I almost got burned, finding it was 150 degrees! I called the owner immediately to inform her, she said that the installer told her that with the temperature setting so high the residents won't use so much HW so they 'should not' run out.

My thoughts; having too much HW is better than not enough - within reason of course.

e-plumber
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"The society which scorns excellence in Plumbing as a humble activity and tolerates shoddiness in philosophy because it is an
exalted activity will have neither good Plumbing nor good philosophy: neither its pipes nor its theories will hold water." -
John William Gardner 10/8/1912 - 2/16/2002

Repair your leaking Plumbing fixtures ASAP [www.theplumber.com]
This slow drip will waste 7+ gallons of water per day.

They do their testing in a laboratory where all the variables are kept constant, not like in the field where they can be changing constantly. In the old days, almost all gas appliances, water heaters and boilers, were rated as 80% efficiency.

And if enough tenants get scalded an go to the hospital there will be fewer users so they should not run out even if they then lower the temperature.

e-plumber
-----------------------------------------------------------------------------------------------------------------------------------

"The society which scorns excellence in Plumbing as a humble activity and tolerates shoddiness in philosophy because it is an
exalted activity will have neither good Plumbing nor good philosophy: neither its pipes nor its theories will hold water." -
John William Gardner 10/8/1912 - 2/16/2002

Repair your leaking Plumbing fixtures ASAP [www.theplumber.com]
This slow drip will waste 7+ gallons of water per day.

I've seen the same philosophy used, but at least there was a mixing valve to temper down the near boiling water... Extra volume good...

Jason

Keep in mind that these spec's come into play only when the water heater is first started or becomes completely depleted.

What they are saying; is if your water heater is completely drained of hot water you should have more hot water in one hour if no one turns on any hot water in the house for next 60 minutes.

2709,9+11

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"mixing valve to temper down the near boiling water"

That's the key phrase.

e-plumber
-----------------------------------------------------------------------------------------------------------------------------------

"The society which scorns excellence in Plumbing as a humble activity and tolerates shoddiness in philosophy because it is an
exalted activity will have neither good Plumbing nor good philosophy: neither its pipes nor its theories will hold water." -
John William Gardner 10/8/1912 - 2/16/2002

Repair your leaking Plumbing fixtures ASAP [www.theplumber.com]
This slow drip will waste 7+ gallons of water per day.