Water Heaters - Dual 50 gal vs. singe 75 gal - HELP

I have owned my new house for about a year. It has TWO 50 gal AO Smith electric hot water heaters. Each heater is on its own 240 volt circuit. The energy stamps on the tank are based on 1994 ratings, so I am guessing they are 1995 models (???). I drain them every few months, and definitely see rust/sediment. Just before the holidays, one of the tanks started leaking around the top electrode.

Since I was gone for two weeks, I shut down the water and power until I could mess with it today. I removed the shot heater and tied the good one directly to the cold water (as it was the first heater in line that died).

My primary question is, do I "really" need two 50 gal heaters? The house is around 4000 sq. ft. and I have three full bathrooms. Right now, it is just me, my wife, and a 6 month old child. We do have frequent visitors from out of town (since we live near Vegas). Should I just run off one 50 gal heater? or get a 75 gal heater? OR just replace the bad one and continue to run dual hot water heaters??? All the plumbing is set for having two, so I guess it is really just a question of electric cost, which is rising quickly although still quite cheap since I live near Hoover Dam.

I would greatly appreciate some insight on this issue. Also, my house is all electric, so gas is not an option.

Thanks!!!

There is no right or wrong decision. If you have plenty of hot water, then there is no need to make an immediate decision. Keep in mind however, when the other heater fails you will be in a hurry for a replacement. The best decisions are not made in haste. If you plan on selling your house then I would replace the failed heater for sure.

Thanks for the prompt reply Jim. It was nice to be able to switch hot water heaters in a matter of minutes (disconnect the broken one) and still have hot water. I read through the forums and noticed a propensity for a Bridson (sp?), but they seemed very difficult to find using a Google search for a dealer. Any other recommendations for a replacement unit? We will run the single water heater for now, but probably will not get a chance to really test it until we have visitors later this year.

Cheers!

Not sure how your tanks are piped in. Lots of times we will set two tanks or more In series. With a shut off on both the cold water and the hot water to each tank. With a cross over from the cold to the hot water above the shutoffs With its own shutoff. This way you can pull any tank out or work on it while the other tank works. You can also cut the power off to the first tank and it will still work as a tempering tank for the other tank.

My tanks are in simple series. Cold water supply is the ONLY shut off right now. If I am messing with the lines, I may go ahead and add some T's to set it up as you explained (good idea). I was just wondering if it is better to just go with a 75 gal or larger single tank or just keep with the twin heater set up. Since I have all the plumbing and electrical in place, I may just keep with two heaters...

Any other opinions or thoughts? I guess keeping two heaters hot will be a lot more energy than just one... or???

Thanks again!

I prefer 2 water heaters as opposed to one big unit. Again, it's a personal choice not really a right or wrong decision. You already found out one of the advantages of 2 units. Other advantages include being able to shut one unit down (I think this was already mentioned) to save energy. 40 and 50 gallon units are sustantially less expensive, much easier to handle and install. I have seen situations where the large unit costs more than 2 smaller units.

Thanks Jim. When using two heaters, do you have a recommendation on how to set the thermostats? Should they be the same? My current set up had the leading heater about 10 degrees or so cooler than the second heater...

Thanks again.

Sure, the leading or #1 heater (for clarity this is the heater that sees incoming cold water and the outlet connects to the inlet of the #2 heater) can be set at a lower temperature. This would allow for faster recovery of the number #2 heater because the water has already been pre-heated. When you expect high demand such as overnight guests, set the #1 at the same temperature as the #2. This would give you a lot more hot water for immediate use. By the same token, if you expect very little usage, you can just shut the #1 off. The nice thing about this setup is flexibility.