I live in a 58 unit condominium building and have been given the task to gather bids from plumbing contractors to replace all 58 water heaters. They are all 11 years old and we believe they could start going bad. The current units are electric AO Smith. They have been great units----have not had any failures to date. The question I have concerns the units' voltage. The voltage to the units is 208 volts, not 220. I am getting opposing opinions on whether the new heaters need to be specifically rated for 208 volts or not. One contractor says the units should be rated at 208 because they will operate more efficiently. Another contractor says it does not have to be specifically rated for 208. He says a 220 volt unit will work just fine. Can someone please attempt to answer this in easy to understand language that I can pass on to these contractors?
Hello: Have a close look at the elements in your current heaters. They are rated at two different voltages. At the lower voltage, recovery of the heater after use is slower than with a higher voltage. But, if what you have now has worked well, there is no need to put in a heater with higher wattage elements. Just match what you have.
Of course, I'd check anodes before simply replacing heaters. I'd also make sure they were on drain pans as they will leak someday
Resistance elements like water heaters are rated for a maximum voltage and power output. For example: 4500 watts at 240 volts.
Power on a fixed resistor is proportional to the square of the change in voltage. Drop voltage from 240 to 208 is a reduction to 0.866 of original voltage. Original power x 0.866 x 0.866 = final power. 4500 x 0.866 x 0.866 = 3375 watts. So it just depends upon how fast you need to recover. Also, 240 volt elements are more plentiful and easier to find than 208. 5500 watts at 240 = 4125 at 208.
Operating below rates voltage will also extend element life. I have my home WH wired at 120 volts for an output of 1125 watts. Of course with a 105 gallon tank recovery is not a problem.
