According to the chart in this http://www.radiantsite.com/files/inf...esidential.pdf Btu output is dependent on the size of tubing used and the spacing of it. For a 1/2 tube spaced 12" apart the Btu output is 10-20h, 9" a part it's 20-30btuh, and 6" it's 30-40btuh. Would adding one length of tubing in each bay increase the Btu output in higher heat loss areas providing that the circuit is the same length as the existing circuits in that zone? Like adding another section of baseboard in series to an existing system.