Those new to designing or troubleshooting hydronic systems often misunderstand how the speed of water flowing through a heat emitter affects heat output.
Call me weird, but one thing I always enjoy is standing in a mechanical room where a circulator is running so quietly that I’d have to put my ear on it to hear any sound.
Aside from the obvious problems caused by poor design or installation, there are several less conspicuous snags lying in wait for unsuspecting hydronics specialists.