The types of commercial HVAC systems you'll work on fall into a handful of families: packaged rooftop units (RTUs), split systems and variable refrigerant flow (VRF), chilled-water plants, boilers and hydronic heating, and the air handlers, VAV terminals and controls that tie buildings together.
This guide walks each one — how it works, the buildings it serves, and what the work looks like — from the <a href="/career-guides/commercial-hvac-technician/">commercial HVAC technician</a>'s side of the trade.
Packaged rooftop units (RTUs)
A rooftop unit is the all-in-one of light commercial work: heating, cooling, and the blower live in a single cabinet that sits on the roof and ducts down into the space.
You'll meet them over stores, warehouses, and low-rise office buildings — anywhere a self-contained unit on the roof beats a basement mechanical room.
The work is the trade's fundamentals in commercial form: scheduled maintenance visits under standing service agreements, plus breakdown calls when a unit quits mid-summer.
Because the equipment lives on the roof, roof access and fall protection are part of the job, not an afterthought.
Our rooftop units guide is the deep dive — the preventive-maintenance and repair tasks techs actually perform, RTU controls and economizers, and the roof-safety rules that apply to the work.
Start there once the basics from this page feel solid.
Split systems and VRF
A split system takes what an RTU does in one cabinet and separates it: the condensing unit sits outside, the evaporator coil and air handler sit inside, and a refrigerant lineset connects them.
Splits come into play where a building's layout or roof can't take a package unit, and conceptually they're a familiar bridge from residential work.
Variable refrigerant flow (VRF) pushes the same idea further: one outdoor unit pipes refrigerant to many indoor fan coils — and in heat-recovery configurations a single system can heat one zone while it cools another.
The piping and brazing have to be right, because the whole system depends on tight refrigerant circuits — and VRF controls differ from one manufacturer to the next, so the brand your contractor installs ends up being the one you learn deepest.
Small packaged units are their own category under the EPA's certification rule: a unit fully manufactured, charged, and hermetically sealed in a factory with 5 pounds or less of refrigerant — packaged-terminal units (PTACs/PTHPs), for example — is a "small appliance," and Type I certification is required to maintain, service, or repair one.
Chilled-water plants
Chilled-water plants move cooling from one machine to the whole building: a chiller makes cold water, pumps push it out to air handlers with chilled-water coils, and the heat collected there is rejected outside through a cooling tower or an air-cooled condenser.
The equipment concentrates in mechanical rooms — basements, penthouses, dedicated plant spaces — instead of sitting on the roof.
Certification matters here in a specific way.
Under the EPA's refrigerant rule (40 CFR 82.161), anyone who could reasonably be expected to violate the integrity of a refrigerant circuit while maintaining, servicing, repairing, or disposing of appliances containing regulated refrigerants must pass an exam from an EPA-approved technician certification program.
EPA's low-pressure appliance class includes chillers using refrigerants such as R-11, R-123, R-113, or R-245fa, and low-pressure appliances are Type III territory; medium-, high-, and very-high-pressure appliances fall under Type II — except small appliances, MVACs, and MVAC-like appliances, which the rule carves out, and small appliances are the Type I territory covered in the split-systems section above.
Our EPA 608 certification guide covers the exam types in full.
This is also where the trade splits into job titles.
Our chillers guide covers what a dedicated chiller technician does — annuals, teardowns, controls work — and who employs them.
Certification rules are federal EPA rules
Boilers and hydronics
Boilers are the heating half of commercial mechanical rooms: they heat water — or make steam — that moves through piping to radiators, convectors, and air-handler coils.
The working fluid is water, not refrigerant, so the day-to-day skills run toward pumps, valves, air removal, and combustion rather than refrigerant charging.
A building can carry both a water side and a refrigerant side — hydronic heating paired with the cooling systems in the sections above — so reading both loops is part of the commercial repertoire.
There is also a plant-side operations role to know about: the International Union of Operating Engineers (IUOE) represents operating engineers, mechanics, surveyors, and stationary engineers, and runs stationary-engineer training.
If the plant room appeals to you more than the service truck, that is the adjacent role to keep in mind.
Air handlers, VAV and controls
The air side is what the building's occupants actually feel.
Air handlers — cabinets holding a fan, filters, and coils — push conditioned air through ductwork, and variable air volume (VAV) boxes modulate how much reaches each zone.
When someone complains about one hot office, the VAV box serving that zone is one of the first things to check, before the RTU or chiller upstream.
Tying it all together is the building automation system (BAS): scheduling, setpoints, and alarms for everything above.
On the data side, BACnet — ASHRAE Standard 135, "A Data Communication Protocol for Building Automation and Control Networks" — is the protocol ASHRAE designed for building automation and control applications such as HVAC control, fire and life-safety systems, security, and energy management.
Where a building still runs pneumatic controls, the gap between pneumatic and direct digital control (DDC) is big enough that it has its own coverage in our controls cluster: start with what an HVAC controls technician does, then the DDC vs pneumatic breakdown.
Controls can also grow into a specialization of its own, with its own credential track — Tridium's Niagara 4 entry course, for example, is called the Niagara 4 Technical Certification Program (TCP), a hands-on course for field service personnel to design, engineer, and program projects on the Niagara 4 Framework.
Which system should you learn first?
Learn the RTU first.
It's the system this page keeps circling back to, and the tasks — filters, belts, coils, airflow, charge — are fundamentals the other systems on this page build on.
Splits come next: the refrigerant cycle and electrical diagnostics carry over straight from residential training, which is exactly what makes them the natural second system.
From there, pick by the buildings around you — chilled-water plants and boilers are the large-building track, VRF matters wherever it has been specified, and controls is its own ladder if the BAS side pulls at you.
Whichever lane you pick, bring the same two things with you: the hours you log on commercial equipment, and EPA 608 in place before you open a refrigerant circuit.
Our how to get into commercial HVAC guide walks the routes in — helper, PM route, residential crossover, or union apprenticeship.