I don't know since plenty of outfits that do mostly residential have little more than hand tools and use primarily flex and ductboard.
It's also the only trade that most are "fully" qualified in. Meaning that while many are also mechanical contractors, they aren;t always full plumber/pipe fitters or electricians. However you often see some companies off plumbing and electrical together with HVAC. It never hurts to diversify your business a little to help with cash flow. HVAC can have all 5 trades. Refrigeration, Plumbing/Pipefitting, Electrical & Controls, SHeetmetal, Mechanical/Millwrights.
The primary HVAC company we use at my work use can often be found also working on baghouses, repairing laterals in ion exchange columns, and changing large coal or corn conveyor belts.