So I am getting quotes to replace my furnace. Looking at variable speed blowers and 2 stage heating. Anyways, I have a 4 ton system, which is the correct size for my house. However, I have 2 trunk lines feeding branches to all the registers. One is 22x8, the other is 12x8. One contractor says that I need to up the size of my trunks about 1/2 the total length of their run to get the correct air flow to all the rooms. The other one says that I have the correct size and dont need to change a thing. What cfm's are those trunks able to handle? I found charts online but the total CFM's come out between 1240 and 1500. My return is also 28x12 if that matters at all.