Hi I have removed one older stand-alone 3 ft convection unit and replaced it with 2 6t sections (12 ft total) of slant fin base board, i hardly get any heat from them . I've bled the line, no air. Are these supposed to be installed with a pitch so the water flows by gravity into the return line so to speak?

A plumber told me there is too much baseboard and water takes the path of least resistance so it goes into the shorter lengths first, is that true?

Thank you

happy holidays

Robert /nyc