I have been in residential A\c and heating for 6 years, i know how to do a proper install with ducts, ID and OD units. Family friend just asked me to do a change out on his 4800 sq ft home on his upstairs unit. I just need a J and D calculation and design to help me out. My question is do NEED a contractors licenses to preform change out? I planned on pulling ALL permits required. May be a dumb question, but i looked everywhere on the internet and could not get answer for it. Thanks!