HJ - I brought up the topic of the spacing between the tees with the B&G rep and he said anything equal or greater than 6 pipe widths (6" in my case) is fine - didn't seem like it's an issue. I understand there is very lttle resistance in a straight run of pipe, but I read on heatinghelp.com it's best to keep the width of the tees the same as the width of the convector so the pressure differential is as equal as possible. Also, from a practical point of view, if the convector is on the first floor, and you drop the risers directly down to basement, easiest to space tees the same width to minimize bends in the risers.
How can I calcuate the pressure drops? I'm not familar with the formula. I will be using a 1" main with 1x1x1/2 B&G monoflow tees, with 1/2" risers to cast iron radiators. There will be a minimum of 4 90 deg bends for each radiator (2x90deg copper bends in basement and 2x90deg brass unions at the rads). My system has been sized for 5.5gpm. Let me know if you need anymore info?