I am planning on adding heat/AC to a sun room that's connected to our family room. The trunk line for the family room side of the house stops at about 3' from the sun room. This trunk line also provides heat/AC to the kitchen, dining room, living room, and the foyer (8 registers total). This trunk line is 16" x 8". Will I be able to take 2 or 3 more supplies from it to heat/cool the sun room? The furnace is a Carrier ICS 58MVC, which should be sufficient to handle the extra 13 x 13 sqft of the sun room. But I am concerned if the heated/cooled air can reach the sun room, since the end of the trunk line is already 38' away from the furnace, and it's another 16' to the sun room window where one of the registers will be.

I got 2 HVAC guys who will do it. One will extend the trunk line to the sun room, and take 3 supplies off. One will just take 2 supplies off near where the current trunk ends. Another guy won't do it, saying there will be no air reach the far end. I am really confused.

I think the questions are: How many supply lines can come off one trunk, and is there a max distance between the register and the furnace?

Thanks in advance!