If you spend time in indoor environments with dirty or poorly maintained HVAC systems, you may be more likely to experience headaches or even migraines. According to one study, 8% of people who work in unsanitary air environments reported having headaches 1 to 3 days a month, and 8% reported having daily headaches. HVAC technicians often have to work with their hands outstretched in the field, and there may be physical demands that are part of their daily life. Technicians may spend a lot of time crouching, bending, or kneeling while installing and working on different types of equipment.
For this reason, it's important for technicians to listen to their bodies and make the necessary adjustments to avoid fatigue. Work conditions can be dirty, dusty, and noisy. There may be tight spaces, and technicians may spend a lot of time on their knees (so it's important to wear knee pads). Additionally, much of the equipment they move is heavy and they're expected to move most of it alone.
Residential work may be more physically demanding since technicians often have to crawl more, but it's not much more difficult than in other sectors. In other words, expect a substantial amount of physical exertion on a weekly basis, but don't worry too much about it. I'm 170 pounds and 6 feet tall and do quite well in tight spaces. The working conditions aren't bad by any means, but it's not easy.
The people who complain that their bodies hurt are usually the ones trying to move a 5-ton compressor across a roof without a wheelbarrow. Your body will punish you if you don't take care of it. Use the right equipment and tools to make it easier to lift heavy loads, and your body will thank you. Like many construction trades, heating, ventilation, and air conditioning can take a toll on your body. You'll likely spend a lot of time standing and you'll have to get into some tight corners.