Most boilermakers learn their trade through a formal apprenticeship program. Candidates are more likely to get into training programs if they already have welding experience and certification. Most boilermakers learn their trade through a 4- or 5-year apprenticeship. Each year, apprentices must have a specified number of hours of related technical training and another large number of hours of paid on-the-job training.

On the job, apprentices learn to use the tools and equipment of the trade. Those who already have welding experience complete training sooner than those without it. In the technical training, apprentices learn about metals and installation techniques, as well as basic mathematics, blueprint reading and sketching, general construction techniques, safety practices, and first aid.

When they finish the apprenticeship program, boilermakers are considered to be journey workers, who perform tasks with guidance from more experienced workers. A few groups, including unions and contractor associations, sponsor apprenticeship programs.
The basic qualifications to enter an apprenticeship program are as follows:

• Minimum age of 18
• High school education or equivalent
• Physically able to do the work

In addition to satisfying these qualifications, candidates with certification or documented welding experience have priority over applicants without experience. A high school diploma or GED is generally required. High school courses in math and welding are considered to be useful.

Workers must be strong enough to move heavy vat components into place. They must have high endurance because they spend many hours on their feet while lifting heavy boiler components. Because workers often work inside boilers and vats, they cannot be claustrophobic. Some boilermakers must work at great heights. While installing water storage tanks, for example, workers may need to weld tanks several stories above the ground.