can anyone help understanding my hotwater heater label?
 

I'm trying to figure out roughly how much power it pulls. On the label it says

watts Upper/SUP 3800/2850 Lower/INF 3800/2850 Total 3800/2850

why the two ratings for each element and why is the total not the sum of each?

Difficult to answer about the dual ratings. Can you provide the manufactuer name and model #.

My educated guess would be the 3800/2850 watts is dependent upon the voltage applied to the element.

watts voltage current resistance
3800 240 15.833 15.158
2854 208 13.722 15.158


As far as "total not the sum of each", water heaters are typically wired so that only one element is on at a time. The top one comes on 1st. Once the top of the tank is hot, the top thermostat move the power from the top element to the lower element.

THanks, that makes total sense. Somewhere I have the wiring diagram for the heater. I'll check to see if it is set up so that both are never on at the same time.

it's a Rheem pe40t9cb00

Hmm I guess that means my estimates of power usage of 5k are far too high. Time to redo the spread sheets.

You are welcome. I could not find any info on your model.

If you want to make your estimate more accurate, measure the voltage and amperage going to the water heater. You should measure it at the breaker panel. Watts = Volts * Amps.

If you do not have a clamp-on amp meter, then use this formula:
Watts = Volts * Volts / Resistance(15.158 from previous post)

The voltage coming into my house varies by 10 volts according to the time of year.

examples:
240v = 3800w
230v = 3490w
220v = 3193w

Over a weeks time that adds up.