water heater question

At a house yesterday with two water heaters. Older water heater no longer used to heat water but supply went to this tank and then to the newer tank. What is the purpose of using the older tank to store water? Cost saving measure? Would the water warm up being in the tank? Could not think of a valid reason for this set up.

I would imagine that the water in the old tank is room temp, let’s say 70 degrees. The fresh water entering the tank is probably about 55 degrees or so. So it’s feasible to think it would take less energy to heat the 70 degree water coming from the old tank (if it is in the old tank long enough to heat up to room temp)

I also think the sacrificial anode in the old tank will continue to deteriorate and contaminate the water going in the newer tank. I would have removed the old tank.


I thinks that’s what the owners were thinking but the heaters are in the basement where it doesn’t get very warm. How much can they save anyway? Besides, the older thank will probably leak eventually.


I agree with Michael Clark. I doubt anyone will be saving any money.

Got a photo (overview, preferably)? It may have been meant as a tempering tank, but was not plumbed correctly.

I could see it being used to pre temper the water. Here the average water temp is about 50-55 degrees. It is quite colder in the winter. Might save $10 a year?

Why isn’t it just that 2 water heaters were installed (for capacity) and found that it wasn’t needed by the current occupant?

Operating the two would have twice the" standby loss" and that is the only way you’re saving anything.

There was no “intent” to do anything. And there’s nothing significant about leaving it the way it is (unless susceptible to outdoor air temperatures).

My two pennies:

I agree with both Michaels. If one tank is old, then both were not installed at the same time. Whatever the reason for this, there was “intent” behind the act of adding a newer tank to the older one. We just do not know what that intent was.

Michael Clark brings up a good point about the sacrificial rod contaminating the newer tank.

For this case, I think the client would extend the life of the newer tank it if stands alone.

When I tell a client to do something, I provide documentation as to what is happening which demonstrates why it should be repaired.

Can you do this for me?

I don’t know that the question by Mr. Anderson was directed to me, but just in case, here it goes.

From his post one can deduce that he thinks there is no need to repair anything, and he might be correct. I don’t know why, however, he would be interested in documenting something he is not about to recommend to his client. His question is academic.

There is nothing intrinsically wrong with plumbing water heaters in series or parallel. In this one case -if I have my facts straight- we have an older, not working, water heater plumbed to a new one. Whatever crud is coming out of the old one goes into the new one, which is not desired, it is to be avoided. That is why the manufacturers recommend emptying the tanks every now and then, to remove sedimentation.

For the above reason alone, I would recommend that he disconnect the older tank. I would also make it clear why I think he should, but I would also add that if he does not want to remove it he should keep an aggressive maintenance schedule to remove sediment.

How to increase hot water quantity using multiple water heaters in series for lower hot water cost

Some buildings use water heaters installed in series to handle variations in hot water demand more economically. Unlike the illustration of parallel water heaters shown above, water heaters connected in series means that incoming cold water flows first into heater #1, then out of heater #1 into heater #2, then out of heater #2 into the building hot water supply piping (or into additional water heaters if more than two are used.)
A synonym for water heaters connected in series is a cascaded water heater design. Cascaded or in-series water heaters is an economical way to handle large variations in hot water demand in a building.

  • When the anticipated hot water demand is low, only water heater #2 may be running.
  • When the anticipated hot water demand is high, water heater #1 is turned on as well, doubling the volume of hot water available (if the heaters are of the same capacity in gallons or liters).
  • Water heater controls can be adjusted so that the “upstream” water heater, (water heater #1 in our example), is left turned off or perhaps set to a very low temperature. In either of these cases, the upstream water heater or tank functions as a “booster water warmer” reducing the energy use by water heater #2 by pre-warming water entering the active heater#2.

It appears to be easier to use the older water heater than change the plumbing. If the older water heater is not leaking than it is just a water storage tank. The water may warm up some but not significantly.
Norm Wild

I agree with Norm. This might be the best solution.

Mike Stone
Orange County Plumber

It is totally confusing and only owner knew the reason behind them.

plumber wayne nj

Great post!!!