A sensible commercial HVAC maintenance program for a small building comes down to three habits: filters changed on a fixed schedule rather than whenever someone remembers, a full cooling inspection in spring, and a full heating inspection in fall. For many offices, shops and restaurants, that works out to a technician on site about four times a year.
Timing matters more in Massachusetts than in milder places. The cooling inspection belongs in April or May, before the first humid stretch puts every rooftop unit in town under full load. The heating inspection belongs in September or October, so a cracked heat exchanger or a failing igniter turns up on a scheduled visit instead of on the first cold Monday morning with customers at the door. Spring and fall are also when the weather is mild enough to shut a unit down for a few hours without anyone noticing.
The maintenance year at a glance
- Monthly to quarterly: filters changed, belts and drains given a quick look.
- Spring: the full cooling inspection, including coil cleaning, drains, the refrigerant circuit and the economizer.
- Fall: the full heating inspection, including the heat exchanger, burners, flue, combustion test and safety controls, plus schedules updated for winter.
Packaged rooftop units (RTUs) are the workhorse for many small commercial buildings, so the checklist below is built around them. Most of it applies just as well to split systems and furnaces in a mechanical room.
The commercial HVAC maintenance checklist, item by item
Filters and belts
Commercial units often hold several filters each, and a building with three or four rooftop units can have a dozen or more filters in different sizes. Choose an interval based on how dirty they actually get, and stick to it. A dusty retail floor, a salon or a busy restaurant dining room sits at the short end. Date each new filter and keep a list of sizes and counts for every unit so the right ones are on hand.
Many rooftop units drive their supply fan with a belt. Belts stretch, glaze and crack, and a slipping belt quietly cuts airflow until it breaks. After that, a unit can keep running its compressor with no air moving across the coil, or keep tripping its burners off on the high limit. Rooftop unit maintenance should include checking belt tension and condition, pulley alignment and bearings at each visit, and replacing belts that show wear. A labeled spare belt for each unit, kept in the building, costs little and can save a second trip.
Condenser and evaporator coils
The condenser coil on a rooftop unit lives outdoors, collecting dust, pollen, cottonwood fluff and, near a kitchen exhaust fan, grease. A dirty condenser can't shed heat, so pressures and power draw climb, the compressor works harder, and on the hottest afternoon of the year the unit may shut itself off on high pressure. Cleaning it each spring with a coil cleaner and a gentle rinse, working from the inside out where the unit allows, is one of the most valuable items on the list.
The evaporator coil inside the unit stays clean only as long as the filters do their job. When filters get skipped or don't fit their racks, dirt mats onto the coil face, airflow drops and the coil can ice over. It should be inspected at every visit and cleaned when it needs it.
Condensate drains and pans
Every cooling unit pulls water out of the air, and on a humid Massachusetts summer day that's a lot of water. It runs to a drain pan and out through a trap. Algae and debris clog the trap, the pan overflows, and the water finds its way into the roof curb or the ceiling below. Stained ceiling tiles are often the first sign. In spring, drains should be flushed, pans checked for rust and standing water, traps confirmed to be the right type and holding water, and any overflow switch tested so it shuts the unit down before water reaches the space.
Economizers and outdoor air dampers
Many rooftop units have an economizer: motorized dampers and sensors that bring in cool outdoor air for free cooling when the weather allows, instead of running the compressor. With our long, cool springs and falls, a working economizer can save real money on cooling.
Economizers are also among the most neglected parts of a rooftop unit. Linkages seize, actuators fail, sensors drift or get disconnected, and nobody notices because the space still gets cooled. An economizer stuck open drags in hot, humid air in July and frigid air in January, wasting energy and risking frozen coils. One stuck closed gives up the free cooling and can starve the space of fresh air. RTU preventive maintenance should include driving the dampers through their full range, checking the actuator and sensor readings, and confirming the changeover and minimum position settings still make sense for the building.
Gas heat sections
Many rooftop units in the area heat with natural gas, and the fall inspection is where the heat section gets its attention: inspecting the heat exchanger for cracks, rust-through and soot, cleaning and checking the burners, making sure the inducer fan and flue path are clear, testing the igniter and flame sensor, verifying gas pressure, and confirming that the high-limit and rollout safety switches work.
A combustion analysis, which samples the exhaust with an electronic analyzer, shows whether the burners are burning cleanly and how much carbon monoxide they produce. A cracked heat exchanger can let combustion gases into the air the unit supplies, so this is not a step to skip. The warning signs are the same ones covered in our guide to carbon monoxide warning signs. If a carbon monoxide alarm goes off in the building, get everyone out and call 911.
Refrigerant circuit checks
On the cooling side, the technician connects gauges or probes to read pressures, superheat and subcooling, measures compressor and fan motor current, and inspects contactors and capacitors, which are common failure points. Federal rules require anyone who services equipment that could release refrigerant, including today's HFC refrigerants, to hold EPA Section 608 certification, and intentionally venting refrigerant is prohibited. OniFix's owner holds that certification.
A unit that needs refrigerant has a leak somewhere; refrigerant doesn't get used up. Topping it off every spring without finding the leak means paying for refrigerant again and again while the compressor runs short of charge part of the season. A good technician will tell you where the leak is, or what it would take to find it, and whether repairing it makes sense for a unit of that age.
Thermostats, schedules and controls
A rooftop unit that holds its occupied temperature all night and all weekend wastes energy every hour the building is empty. Check that each thermostat or controller has the right occupied and unoccupied schedule, with setbacks for nights and weekends, holidays entered, and clocks correct after daylight saving time changes and power outages. If your business hours changed since the system was set up, the schedule probably didn't.
Two other settings deserve a look. In many buildings the supply fan is meant to run continuously during occupied hours so ventilation air keeps coming in; set to Auto, it only moves air while the unit is heating or cooling. And thermostats in shared spaces often need limits or locks, so nobody sets one unit to 80 while the unit next to it is cooling.
Roof curbs, panels and access
Walk around the outside of each unit. Access panels with missing screws or torn gaskets leak air and let rain in. The flashing where the unit's curb meets the roof is a frequent source of leaks. Gas piping on the roof should be properly supported and free of heavy rust. And someone has to be able to reach the units safely: a working roof hatch or ladder, a clear path across the roof, and, after a big snowstorm, intakes and flue outlets cleared of drifts.
Ventilation for the people inside
While the building is occupied, rooftop units bring in a set amount of outdoor air, based on code requirements for that type of space. That minimum is set at the economizer or outdoor air damper, and it drifts when dampers stick or someone closes them to cut heating bills. Too little outdoor air shows up as stuffiness and lingering odors. Too much shows up as drafts, high bills and clammy air in summer. Some units adjust ventilation using carbon dioxide sensors, and those sensors need checking too. Restroom and other exhaust fans belong on the list as well, since a dead exhaust fan changes how air moves through the whole building.
Restaurants and commercial kitchens
Kitchens add a piece of equipment most offices don't have: the make-up air unit. A kitchen exhaust hood pulls a large volume of air out of the building, and the make-up air unit replaces it, usually heating it in winter. When make-up air fails, or gets shut off to save on heating, the building goes into negative pressure. Doors become hard to open, cold drafts pour in around them, the hood captures smoke less effectively, and in the worst case gas appliances and water heaters can have their exhaust pulled back into the building. Make-up air units deserve their own spring and fall checks: filters, belts, burners and the interlock that starts them with the hood.
Grease is the other kitchen problem. It coats condenser coils near the rooftop exhaust fan and loads filters faster. Cleaning the hood and the grease duct itself is a separate, specialized job usually handled by a hood cleaning company, but the HVAC schedule should account for the extra grease on everything nearby.
Keep records, and plan around business hours
A simple log for each unit pays for itself the first time something breaks. Record the make, model, serial number and age, the filter sizes and counts, belt sizes and refrigerant type, and keep a dated note from every visit with what was found and what was done. Records let a technician spot a trend, like a compressor drawing a little more current each year, and they're what you'll want in hand when deciding whether to repair or replace an aging unit. They also help if a part fails under the manufacturer's warranty.
Most maintenance doesn't need to interrupt business. Filter changes and visual checks can usually happen while you're open. Work that shuts a unit down, like coil cleaning or a heat section inspection, can be scheduled before opening, after closing or on your slowest day, and staggered so the space never loses all of its heating or cooling at once. When you book commercial HVAC service, mention roof access, keys, alarm codes and any areas that can't be disturbed, and let your staff know a technician is coming.
OniFix maintains and repairs heating and cooling equipment for offices, shops, restaurants and other businesses in the towns we serve west and north of Boston, with the price given before any work starts. If you'd like your rooftop units looked over before the next season, start with our commercial HVAC page.
Sources: EPA, Section 608 Technician Certification; EPA, Stationary Refrigeration and Air Conditioning (Section 608).