I have posted the whole supply layout. the unit is in the basement and feeds the registers in the floor. It is not the best system but its a 100 year old house. Money is very limited so i have to do it myself. its a 46k btu 1200cfm system in a 1300 sq ft house. Is the unit big enough? would a 1600cfm system be better. There are 2 returns in the ceiling listed in the pic but they are not of concern. I just want to make sure i am not sizing the duct improperly. I want to use 12" metal pipe instead of square supply branch, but i can use square if its better. maybe 12" is to small? the 10x15 is the kitchen 8x7 and 12x7 are bathrooms. the reason i have 12" to 10 flex is the back bedroom and bathroom were an addition and there is a only a tight spot to get the duct through. any help would be greatly appreciated.