On Monday, February 4, 2013 2:56:03 PM UTC-5, TomR wrote:
PrecisionmachinisT wrote: "Existential Angst" wrote in message ... wrote in message ... A friend has a house that came with two identical water heaters hooked up in parallel. He doesn't need all the capacity, so we turned one of them off and turned off the water going into it. This was several years ago. The water heater was about 4 years old at the time, it's now 7 years old. Given that a tank has already had some service, what would you guys do to try to keep the spare tank available for as long as possible? Leave it full of water? Drain it? My thought was that draining it would be worse, because allowing air in, it would rust....... Fill it with water, add a rust inhibitor? As an aside, shouldn't two water heaters be hooked up in series? Been meaning to post that to the group. The rcm peeple should have some insights into both Qs. Having a second tank that's unpowered, uninsulated, and plumbed in series so that cold water passes through it first will reduce summertime AC and water heating costs by naturally warming the inlet water up to room temp. I am not sure, but I think that technically speaking that approach won't save any money on energy costs. The reason is that for the water in the first tank to be brought up to room temperature, it needs to draw its heat energy from the room. So, it will cost that much more to heat the room because some of the room heat is going toward heating the water in the first tank. In other words, there is no free heat -- it either gets its heat from being heated by at working hot water tank, or it gets its heat from the room and that heat energy needs to be replaced by the heating system for the room.

I believe he said "reduce summer time costs". And it does do that since ground water and city water are usually a lot cooler than summer air temps.

I run two wh in series with the 1st one on a 30amp switch in the hall. When I anticipate guests or otherwise needing extra hw I just turn it on.