Commercial HVAC maintenance schedule for rooftop units

This post sets out which tasks fall where, what each seasonal visit adds, and when to do more than the minimum. For what to check on each visit, see our rooftop unit maintenance checklist. For the wider picture, see our guide to commercial HVAC maintenance.

How often does a rooftop unit need maintenance?

Twice a year at a minimum, often quarterly. NREL's 2025 rooftop unit maintenance guide groups tasks into quarterly, semiannual and annual. A York commercial manager writing in ACHR News described quarterly and semiannual service as common, with visits at the start of the heating season and again at the start of the cooling season.

ASHRAE/ACCA Standard 180, the US standard for maintaining HVAC in commercial buildings, doesn't set a visit frequency. It sets a minimum frequency for each task, from monthly to annual. So a quarterly contract and a twice-a-year contract can both meet it, as long as each task is done as often as its table says.

The manufacturer's instructions for the unit come first. NREL says to start there and follow Standard 180 on top.

Which tasks are quarterly, twice a year and annual?

This table uses the frequencies in NREL's guide (adapted from Standard 180-2018) and the Standard 180 equipment tables. Where they differ, both are shown.

On a twice-a-year contract, the quarterly tasks either need extra visits or need someone on site to do them. Filters are the usual example. If in-house staff change filters between contractor visits, it helps to log it in the same place as the PM work orders.

What gets done on the spring visit vs the fall visit?

Most of the list applies to both. Contracting Business lists most rooftop unit tasks "at the beginning of each heating and cooling season": filters, coils, belts, fan bearings, the economizer and the refrigerant charge. Each season then adds a few of its own.

Spring: cooling start-up. Check and clean the condensate drain at the start of the cooling season (Contracting Business). The unit runs in cooling mode for this visit, so it's when the cooling-side checks get done: condenser coil, refrigerant charge, amps and the temperature drop across the coil. The yearly condenser coil cleaning usually fits here.

Fall: heating start-up. Inspect the flue passages, the burners and the combustion air blower, and test the temperature limit switch (Contracting Business). Standard 180 calls for testing and adjusting combustion once a year, so this is when that happens. NREL also lists a quarterly look at the burner itself.

Our checklist has the detail for each item.

What do heat pumps need before winter?

Heat pump rooftop units need the same maintenance as gas units, plus a few heating-side checks. NREL lists them:

• Heating sequence. Check heating, backup heating and defrost run in the right order, especially where the heat pump and the backup heat can run at the same time.
• Lockout and restart setpoints. Check the outdoor temperatures at which the heat pump locks out and restarts. NREL says the right values depend on climate zone and how the system is set up.
• Defrost and drainage. The outdoor coil makes condensate in heating mode, even below freezing, and the unit runs defrost cycles to stop ice building up. Check the freeze protection and the condensate drainage regularly.
• Compressor. A heat pump compressor runs more hours than one in a cooling-only unit. NREL says that makes compressor inspections more important and more frequent.

Doing these on the fall visit means problems show up before the unit has to carry the heating load.

Are these frequencies enough for every site?

No. Standard 180's frequencies are minimums, and NREL says PM should be tailored to the location and to the size and age of the unit. Three kinds of site usually need more:

Dusty sites. FEMP's guide puts filter changes anywhere from monthly to every six months, depending on how much dirt is in the air.

Kitchen exhaust. Units near restaurant exhaust fans pick up grease on the condenser coil. Trane says to clean the coil at least once a year, more often in dirty locations.

Coastal sites. Carrier's air conditioner service manual treats anything within 2 miles of the ocean as a coastal environment, because salt travels that far as spray, mist or fog. Trane's coil coating literature for rooftop units says airborne salts shorten the life of air-cooled coils. Carrier's advice is to inspect the coil and base pan often, especially after storms and high winds, and to rinse the coil as often as inspection shows. It also warns against high-pressure water, which can damage the fins.

Hot, humid climates add to this. In Florida the cooling season runs for most of the year and the condensate drain stays wet almost all the time, so drain checks matter more. Our post on what Florida's climate does to commercial AC covers this.

How do you run a PM schedule across many sites?

Usually the schedule sits in a CMMS (computerized maintenance management system) or another work order system, with a PM work order per unit per visit. A few things help when the units are spread across many locations.

Write the frequencies into the contract. NREL's guide says a service contract should state which equipment is covered, which tasks are done, and how often. It also suggests stating what report you want after each visit.

Keep the readings. NREL recommends keeping a detailed log of the work done. Amps and temperatures from the spring visit give the fall tech a baseline for the same unit.

Know what you have. NREL's guide gives Arby's as an example: the company built its own phone app to inventory its rooftop units and record their condition across the whole fleet.

If you use a contractor, our post on commercial HVAC preventative maintenance contracts covers what a contract usually includes and what to ask.

What happens between scheduled visits?

A schedule covers the units on the days someone is on the roof. A 2004 PNNL paper on rooftop units found that faults like low charge or a stuck damper usually don't cause complaints, so they "are not generally reported nor are they corrected". They can run until the next visit.

SmartHVAC monitors rooftop units, split systems and commercial heat pumps between visits, around the clock. When a unit starts running differently, your team sees it and decides whether it needs a work order, can wait for the next PM visit, or needs nothing. To see how it would work on your units, book a demo.