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Author:
tomden (NY)
I am try to see how many gallons my new electric HWH (says 38 gallons) actually holds/heats up when just filled with cold(45deg) water and how long it should take. it's rated at 4500W. I have come across this 70% number but don't know if that applies.
I was checking the electric meter and it user approx. 8 kwh (little else in the house was running).
It took approx. 1.5 hrs to heat (I was watching the meter and could definitely see when it stopped). Does that sound right?
Thanks
Tom
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Author:
tomden (NY)
Packy
Thanks. I'll use those formulas. But when I calculate gallons to be heated is a 38 gallon WH actually heating 38 gallons? I see this reference to 70% number cutting the 38 to 26??? Should I use 38 for the formulas or 26.
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Author:
packy (MA)
yes.. the 70% number is the approximate number of gallons of usable hot water before you start drawing water that is not as hot as when you started.
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Author:
tomden (NY)
I'm still not sure. If I heat a 38 gallon HWH for the first time am I heating 38 gal or 70% of 38 gallons.
Thanks
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Author:
packy (MA)
you are heating 100% of the water plus on initial startup the walls of the tank are very cold and they will need to be heated as well.
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Author:
NoHub (MA)
The cold water going to the bottom of the tank and mixing with the hot that is there...thats why you only see about 70% of the hot water in the tank.
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Author:
hj (AZ)
When you start heating you are heating ALL 38 gallons, but as it operates the water is getting warmer and so you are NOT heating it to the same degree as when you started. Therefore, the heating time is more a curve than a straight line.
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Author:
stuckinlodi (MO)
The water heater manufacturer has the number for what they call a "recovery" rate, which is the number of minutes needed for the water heater to heat the water inside the tank to the temp setting on its thermostats. The upper and lower heating elements will heat their part of the tank to the setting temperature, so when done the entire tank of 38 gallons is close to the temp setting. But as you use the hot water you will have cold water comes in to replace it, so naturally the temp of the water in the tank will start to decrease. At some point the water in the tank will drop below the thermostat setting and the heating element will switch on. The time to heat the water depends on the wattage of the heating element and the temp of the cold water coming in. In winter time it will take longer to heat a tank of cold water than in summer because the temp of the water coming into the tank is lower in winter time.
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