This is my first time posting here, so please be very kind! I am getting an addition put onto my house that will add apporxiametly 450sq ft of living space. My current system (heat pump)is 17 years old, and I am looking to repalcement the system and upgrade it to the size needed to supply the addition as well. I ahve had a few different HVAC people come out to look at how the new feed lines could get ran to the new rooms. One wants to go up through my main floor into the attic and over to the new room, which would be ceiling mounted ducts. I really don't want to do this because it would be going through my sons room (which is already tiny to start). I had someone come out last night that said he could branch 2 7" feeds from the current trunk line (which is 10" x 18") into the new addition (16'x20' in the main room size). My question is the distance from the main trunk line to where the new feed line would be is about 26'. Id this to long of a run through a 7" pipe? The room faces south and I live in Maryland. I wuld go up through the attic if that would yeild me the best option (the other contractor was going to add a new trunk line into the attic and then branch off of it). Please let me know if more info is needed. Thanks!!