21 years on my own, been at it for 26 years, my Dad and my Grandfather were heating contractors. I was threading pipe by hand and helping my Dad as far back as I can remember.
In the summers I would help him retrofit those old Nesbitt RMA100 Multizone Rooftops, he was the Nesbitt Service guy for the eastern 1/2 of the US, he took me along so he wouldn't have to crawl up into the hotdecks to install the wiring and sensors.
23 years + a 3 year stint in the Navy. HVAC has been my prime experience but I'm also proficient in building remodeling, woodworking, carpentry, electrical, and plumbing, due to having learned and practiced these trades in the facilities maintenance/management fields.
You can never know enough about any of it but the fun of learning about all of it never stops.
Electricity makes refrigeration happen.
Refrigeration makes the HVAC psychrometric process happen.
HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.
A building is NOT beautiful unless it is also comfortable.
I been in the pen for 15 years now. Probably will never get out. Residential, then light commercial/refer, then stationary engineer, back to light commercial, Now stationary hvac, I'll keep you posted since I get bored quick.