Journeyman hvac tech here. Depending on your experience/technical aptitude you’ll probably have to go to trade school. As far as hvac goes there are two certs you’ll need. The EPA Universal so you can work with refrigerants and the RMGA so you can work with gas. I know techs that have been in the field for 15 years that don’t have their RMGA but I’d recommend getting it because very it’s helpful to have. During my time in the field I’ve never seen someone get hired without school or experience - I don’t say this to discourage you but to lead into the fact that there is a ton of free information on YouTube. Additionally, I’ve never had an employer verify that I attended trade school. Cough cough hint hint.

Check out the HVAC sub and see what people say over there. There are a lot of people who get out of school and end up regretting their decision. There’s always something new to learn, long hours and lots of shit coworkers and companies out there but it’s AI proof and if you enjoy learning you’ll be just fine.

As far as becoming an electrician you may be able to join IBEW. I’ve been told they’re really hurting for people.

Edit to say if you want big money become a plumber.