Well, you've got a few things going on here.
First, the Johnson pump is a direct drive, versus the Eheim's magnetic drive, so the Johnson is going to be more efficient (but alas, not more reliable!)
From other users of "the Johnson", the power draw does vary with the load. I believe Since87 ran some tests that way, among others. Other reported results are similar, for other pumps.
So I'd have to go with: "It's a max rating".
|