Installing 2 electric heaters

[Jrahn]

I have 2 AO Smith Pro Max electric heaters, I need more hot water available. I would normally opt for parallel installation. However, the units are of different capacities. 1 is an 80 gal and the other a 60.
Series seems the best option, which should be first in line?

Also, does each unit need its own expansion tank?

Thanks!

[hj]

I NEVER use a parallel installation, always a "series" one. Use the oldest tank first, since the first one will fail first. Other than that it makes no difference which is first. One expansion tank after the water shutoff is all you need.

[Jrahn]

Thank you!
The tanks are the same age. Just wasn't sure if the smaller should feed the larger or vice versa

Also should my Watts recirculator pump be on the second tank?

[Hackneyplumbing]

The first tank does the majority of the work in a properly sized series system. Each unit does not have to have its own expansion tank. Size the expansion tank according to the total volume of hot water your storing.

[hj]

CXonect the pump to the first tank, that way the whole system will be at the same temperature, regardless of any fluctuations in operation between the two tanks. The 60 gallon tank may be the more expensive one to replace so put it second. The first tank will get MOST of the precipitation out of the water so it will fail first. You may replace the first tank several times before the second one fails.