Great question! After a lull in enrollment in vocational schools during the 1990's - 2010's, employment in the skilled trades is increasing. While your local community colleges or accredited technical schools are always a great path, but the best way would be to speak with a professional or contractor in the HVAC field. Ask which skills and training they look for in a potential apprentice or new technician. Tailor your learning to what the actual demand is in your field. Applying to skilled trade unions always holds potential for growth and experience as well.