HVAC is central to building comfort. Heating, ventilation, and air conditioning control temperature, humidity, and indoor air quality so people can work without thinking about it. When these systems break, productivity goes down, and energy bills go up.
This guide describes the major components of a commercial HVAC system—what they do, how they impact efficiency, where they typically fail, and how to maintain them. If anything in here sounds familiar, mark it for your next service visit. Book your HVAC inspection or get a quote for upgrades.
What is an HVAC system?
An HVAC system transports air and heat. It is heated during winter (furnace, boiler or heat pump). It chills during the summer (refrigeration cycle). It introduces new air (ventilation). And it provides conditioned air in the right place (air handlers, ducts, and terminal units).
Controls range from a wall thermostat to a complete BAS / BMS. They begin with equipment, capacity, and airflow to demand.
Thermostats & Controls
Thermostats measure room temperature (and in some cases humidity and CO 2 ) and indicate to the system when to heat, cool, or ventilate. In commercial buildings, more than one sensor may report to a BAS that has setpoints, schedules, and alarms.
HVAC energy consumption can be reduced by 10-30% by means of occupancy-based control, smarter setpoints and tight schedules. Wins on low cost include:
- Outdoor-air reset
- Demand-controlled ventilation (DCV)
- Optimal start/stop
Typical failure points:
- Dead batteries, loose wiring, or failed relays
- Sensor drift or bad placement causing comfort complaints
- Locked-out schedules that run equipment when nobody’s there
Verify sensor calibration annually, check locations (eye-level, away from drafts), review schedules each season, and trend data. If you’re still on old pneumatic or standalone stats, it may be time to get a quote for networked controls.
Furnace or Heat Pump (Heating Side)
Furnace employs gas as a fuel to heat up heat exchanger; air is circulated over the exchanger and gets warmed. Condensing furnaces also use additional heat present in the flue gases to improve efficiency.
Heat pump, on the one hand, transfers heat with the help of a refrigeration cycle. When in heating mode, it removes heat in the outdoor air or ground and provides it to the indoors. Variable-speed compressors are frequently used in commercial units.
Some of the failure points of furnace include cracked heat exchanger (safety risk), ignition or flame sensor problems, flues that are blocked, and inducer motor failures.
Heat pump has certain points of failure such as leakage of refrigerants, reversing valves, defrost board, and outdoor fan motors.
Maintenance advice would be annual combustion analysis of furnaces, crack inspection and proper venting. In the case of heat pumps, ensure charge through superheat/subcooling, ensure defrost is working, and maintain clean outdoor coils. When heating bills are skyrocketing, it is time to schedule HVAC inspection and compare repair and upgrade.
Evaporator Coil (Cooling Side)
The evaporator coil sits inside the air handler. Warm return air passes over the cold coil. The coil absorbs heat and moisture. The supply air leaves cool and dehumidified. A TXV or EEV meters refrigerant to the coil.
Keep the coil clean and the refrigerant charge correct. Even a 10% drop in airflow—or a dirty coil—can cut capacity and raise compressor energy use.
Smarter metering and improved coil design help at part load and tighten humidity control.
Typical failure points:
- Refrigerant leaks at U-bends or due to corrosion
- Icing from low airflow or undercharge
- Condensate drain clogs leading to water damage and microbial growth
Replace filters on schedule, clean coils and drain pans, confirm airflow and static pressure, and test the float switch. Seeing water stains near an air handler? Don’t wait—schedule HVAC inspection.
Air Handler & Blower Fan
The air handler contains the fan, filters, the heating/cooling coils, and possibly outside-air dampers. It pulls in air, conditions it, and blows it through ductwork. Fans may be belt-driven or direct-drive, increasingly with variable frequency drives (VFDs).
Fan power scales fast with speed (affinity laws), so even small speed reductions save a lot. VFDs and pressure reset strategies cut energy and noise. Right-sizing filters and ductwork lowers static pressure, improving efficiency.
Typical failure points:
- Belt wear or misalignment, loose set screws, bearing failures
- VFD faults from cooling issues or electrical noise
- Dirty filters driving up static and energy use
Track filter pressure drop, inspect belts and bearings, balance fans, and keep VFDs clean with adequate cooling. Trend supply fan speed vs. static to spot drift. If static pressure stays high, get a quote for duct corrections or fan re-selection.
Terminal Units (VAV Boxes, Fan Coils, Reheat)
Terminal units fine-tune conditions zone by zone. VAV boxes throttle airflow with dampers. Fan-powered boxes add a small fan to blend return/primary air. Reheat coils (electric or hot water) warm air for individual zones. Fan coil units or cassette units serve rooms directly.
Zoning avoids conditioning empty spaces. VAV reduces fan energy; reheat should be minimized with good supply-air temps and sequences. Leaky hot-water valves or mis-set minimum airflows waste energy silently.
Typical failure points:
- Stuck or hunting dampers, failed actuators
- Dirty fan coils, noisy or worn small fans
- Faulty or overridden temperature/flow sensors
- Reheat valves stuck open
Calibrate airflow stations, verify damper travel, test reheat valves, and clean fan coil filters. Seasonal recommissioning pays back quickly. Book a scheduled HVAC inspection if one zone is always too hot or cold.
Ductwork
Ducts distribute supply air and return it to the air handler. Think of them as highways for conditioned air.
Leaky or poorly insulated ducts lose air and heat. High static from tight turns, crushed flex, or undersized trunks forces fans to work harder, raising energy use and noise.
Typical failure points:
- Leaky joints, missing sealant or tape failures
- Damaged or sagging flex duct
- Poorly balanced dampers causing hot/cold spots
Test and seal leaks (mastic > tape), add or repair insulation, straighten runs, and perform test & balance after major changes. If your fan runs hard but rooms still complain, get a quote for duct assessment.
Advanced Option: VRF/VRV Systems
Variable Refrigerant Flow/Volume systems use inverter-driven compressors and refrigerant piping to serve many indoor units from a few outdoor units. Heat recovery variants move heat from zones in cooling to zones that need heating at the same time.
Outstanding part-load performance, strong zoning, and heat recovery reduce hours on boilers and electric reheat. They often shine in buildings with diverse loads—think offices with sunny and core zones.
Typical failure points:
- Refrigerant leaks (long piping runs raise the stakes)
- Control network errors between indoor units and the outdoor controller
- Oil return issues if piping and commissioning aren’t done right
Maintenance tips include strict adherence to manufacturer piping rules, regular leak checks, clean strainers and EEVs, and software updates. Staff training is non-negotiable. Considering VRF for a retrofit? Get a quote and ask for a life-cycle cost comparison, not just the first cost.
Fresh Air with Less Waste: HRV/ERV
Heat Recovery Ventilators (HRVs) and Energy Recovery Ventilators (ERVs) pre-condition outdoor air using exhaust air. HRVs transfer heat. ERVs transfer heat and moisture. You get fresh air with less load on your heating and cooling equipment.
Expect significant ventilation energy savings and better humidity control. ERVs help in humid climates by reducing moisture brought indoors; HRVs fit colder, drier climates.
Typical failure points:
- Dirty filters and plugged cores reducing airflow
- Frost/defrost control problems in cold weather
- Failed wheel drives on rotary ERVs
Clean or replace filters, wash cores per manufacturer guidance, verify wheel rotation and seals, and confirm defrost operation. If occupants complain about “stuffy” rooms, check ventilation rates and schedule HVAC inspection.
BAS/BMS: The Glue That Makes It Smart
A building automation system ties everything together. It gathers sensor data, runs sequences (economizer, resets, demand control ventilation), and raises alarms. With trend logs and analytics, it spots issues before people do.
Efficiency impact:
- Optimal start/stop avoids conditioning empty buildings.
- Static pressure reset lowers fan energy.
- Hot/chilled water resets trim boiler and chiller loads.
- Fault detection & diagnostics (FDD) catches things like simultaneous heating and cooling or a stuck damper.
Typical failure points:
- Overrides left in place, masking real problems
- Out-of-date graphics and undocumented changes
- Failed sensors feeding bad data to good logic
Review trends monthly, clear overrides, test alarms, back up controllers, and keep a change log. Add CO₂ and occupancy data where it helps. If your BAS is more “set and forget,” it’s time to get a quote for tuning or an analytics add-on.
Quick Maintenance Checklist
Replace or inspect filters, check drain pans and pumps, walk ducts for damage, confirm BAS schedules. Clean coils, verify fan belts and bearings, test economizer and dampers, calibrate a sample of sensors.
Commission setpoints and resets, test heating/cooling changeover, verify heat pump defrost, validate reheat logic, and balance critical zones.
Also, leak-check refrigeration systems, test combustion safety, review trend data for chronic issues, and plan capital upgrades.
If you’re not sure where to start, a preventive plan with clear tasks and intervals will save more than it costs. Want help building that plan? Schedule HVAC inspection. Looking at upgrades like VFDs, ERV, or VRF? Get a quote with energy savings and payback laid out in plain numbers.
Read More: Summer Maintenance Tips for Your Air Conditioner
Bottom line
Commercial HVAC is not a single large box; it is a group. The thermostats are the quarterbacks, the heating and cooling equipment are the brawn, the air handlers and ducts are the workhorse, terminal units ensure the zones are optimized, and a BAS makes everyone accountable.
Maintain the components clean, adjusted and synchronized and your building will feel good, cost less to operate and will complain a lot less. Once you are ready, book HVAC inspection or request a quote to seal the performance.
FAQs-
What are the 5 main components of an HVAC system?
The main components include the thermostat, furnace or heat pump, evaporator coil, condenser coil, and ductwork.
What are the major parts of HVAC systems?
Along with the primary five, components like air handlers, compressors, expansion valves, and air filters play a crucial role in system efficiency and comfort.
What parts make up an air conditioning system?
An air conditioning system is made up of the evaporator coil, compressor, condenser coil, expansion valve, and blower fan
How do I know if I need HVAC repair?
Look out for warning signs such as uneven room temperatures, weak airflow, strange noises, or increasing energy bills.
Why is ductwork important in HVAC systems?
Ductwork acts as the highway for conditioned air. Any leaks or blockages can cut efficiency and compromise indoor air quality.
