I want to kno a easy way to figure out what size duct board to run on an install. this is how I was taught please set mme straight.
1. start with the size of the opening above the furnace,( on a typical updraft unit say 3 ton
2. make that extend into ceiling .
3. then make trunk duct 12-14 square
4 take offs are 7" take off with flex for 800-1000 squre feet and adjust acordig to squre feet and heat load from there.
I am a good refrigeration tech and a/c troubleshooter but need help with duct work. can some one help me out.