Yesterday, I replaced the thermostats on my water heater, and since I had to turn the power off for that, I decided it would also make sense to flush it since it’s about 6 years old. Anyway, drained it completely, ran cold water through it for about 10 minutes, then filled it back full of cold water, and turned on the power.
I was kind of surprised that it took over an hour to completely heat the water. Then today, I started thinking about it and thought “wait a second! I minored in chem. I should be able to calculate this”. So, let’s see what we know, and then do some basic math!
Knowns:
- Water heater size is 50 gallons
- Element size is 4500 watts
- Incoming water temp (ground water) is 61F (right now)
- Water heater thermostat is set to 115F
Since we’re dealing with Imperial units here, we’ll stick with them (as painful as that may be).
- 1 gallon weighs 8.345 pounds (lbs)
- 1 watt/hour is equal to 3.412 BTUs
Quick definition of BTU: “The quantity of heat required to raise the temperature of one pound of water one degree at a constant pressure of one atmosphere”.
