How long does it take to become certified hvac?

Certified by whom? If you are going to take a test for a certain certification, as soon as you pass that test you have gotten that certification. If you are enrolled in a program, however long that program is scheduled to complete will be your answer, assuming you pass the test upon completion. The UA Local 475 AC/Ref Division apprenticeship program here in NJ is 5 years, during which you are working full time in the field as an apprentice and attending class. But understand there are many other programs (public and private tech schools/ day and evening classes) out there of various lengths and accredations so there is no one answer. Plus different States also have different requirements. Confusing? Make your parents happy, go to Med school. If you dont care what others think of you go to Law school.