Residential and some light commercial HVAC. Change outs, new construction, remodels. Didn't go to school for any of it, but I've been around it most of my life because my dad and uncle had a business doing it when I was growing up. I like it, the new construction part can get kinda boring for me, but I ejnoy changing out existing equipment in people's houses.
I also have an ass load of certifications for road construction. If I ever wanted to, I could get a job as an inspector for a DOT, but I'm over that kind of work for the time being.