I'm not so familiar with hydronics (just did my first project), but I assume that where there's a small imbalance, there's a difference in flow and thus less heat given--it's not all or nothing.

I'm not sure why you say that. First, I'm not convinced that the OP intended the diagram to be to scale; maybe the installation is entirely symmetric, but drawn with longer pipes to Tank 2 simply to make it fit easier in the diagram.

But even if the drawing is to scale, I marked it up below to show the imbalance. Below the black line is the section where there are two parallel paths. And the green piping represents the extra piping to Tank 2; if you deleted that piping, it would be balanced.

[Exactly so on the hot side; on the cold side, I assumed that the cold tee has Tank 2 on the straight path, and Tank 1 on the side outlet, and that the equivalent length of "straight path of tee plus 90" is less than the equivalent length of "side branch on tee", so the non-green piping after the tee represents that difference in equivalent lengths.]

So maybe worst case the piping to Tank 2 is twice as long? It depends on what equivalent length, if any, should be assigned to the tank itself. I already did the math for the case that the Tank 2 path is 50% longer; if it's twice as long, then the flow through Tank 2 should be sqrt(1/2) = 70% of the flow through Tank 1.

Cheers, Wayne

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