When designing hydronic circuits, most of us focus on what’s necessary for that circuit to absorb thermal energy at a heat source, carry it along like a conveyor belt and release that energy at one or more heat emitters.
Have a look at the rating tables for most finned-tube baseboard sold in North America and chances are you’ll see a footnote under the table that reads something like this: “Ratings are based on active fin length and include 15% heating effect factor.”