I would check with A.O. Smith at www.hotwater.com but 1500w is VERY small for a 50 gal water heater. I sell & install water heaters for a living, and never install less than 4500w elements (usually 5500w) & 7000w in my tankless heaters. Look at the information plate or label on your heater, it'll tell you what was originally installed. 1500w will work, but it'll take forever to heat your water, unless you live somewhere tropical. If your circuit breaker is 30amp, and wiring is #10 sheathed electrical cable, you can safely install 5500w elements in both top & bottom. I still suggest checking with AO Smith. Happy new year & best of luck. P.S. this is a good time to flush your tank, and get rid of some of that sediment that's built up. Cheers, Brian (in cold south Louisiana). Hey John 2000, I'm going to attempt to quit Woodbines tomorrow.