Preventive maintenance saves money on commercial HVAC because rooftop units fail in slow, predictable ways: a belt goes slack, an economiser actuator seizes, a condensate trap dries out, a filter rack loads up. Every one of those is a scheduled visit item and every one becomes an after-hours call if nobody looks. Most GTA buildings want two full seasonal visits plus filter and belt checks each quarter — restaurants and shops with airborne dust need more.
Rooftop Units Fail Differently Than Home Furnaces
A residential furnace sits in a conditioned basement and moves air through short ducts with a direct-drive blower. A packaged rooftop unit sits in full weather on a curb, usually runs a belt-driven blower, carries its own condenser and gas heat section in the same cabinet, and takes in outdoor air through a damper assembly. That is four more failure paths, all of them exposed to freeze-thaw, roof grit and, along the QEW and 403 corridors, industrial dust.
It also means the failures are invisible until they are expensive. Nobody notices a belt at half its tension; they notice the day the blower stops. Nobody notices a curb seal lifting; they notice the ceiling tile stain under the unit. If you are weighing whether an aging unit is worth maintaining at all, our RTU replacement guide for Toronto property managers sets out where that line sits.
The Economiser Is the Most Expensive Part Nobody Checks
The economiser is the damper section that brings outdoor air into the unit for free cooling when conditions allow. Its actuator, linkage and outdoor-air sensor live outdoors and fail quietly, and they fail in two directions.
Stuck open in January, the unit tries to heat outdoor air at -12°C every time it runs, the gas section works flat out, and the coil sits at risk of freezing. Stuck closed in May, you pay for mechanical cooling on days when 14°C outdoor air would have done the job for the price of running the fan. Neither condition throws an alarm on most units, and both show up on the utility bill months before anyone connects them to a linkage that costs very little to free.
What Belongs in a Quarterly Commercial Visit
- Filters changed and the rack checked for bypass around the media — a gapped rack sends unfiltered air straight onto the evaporator coil
- Belt tension and deflection measured, sheaves checked for wear and alignment, and a spare belt left on site
- Motor and bearing condition checked by amp draw and by feel; grease points serviced where fitted
- Economiser damper stroked through its full travel, linkage freed, actuator and outdoor-air sensor verified
- Condensate pan cleaned and the trap primed — a dry trap on a draw-through unit lets the fan pull air backwards and flood the pan onto the roof or the ceiling below
- Condenser and evaporator coils cleaned, and the curb, flashing and gasket inspected for water entry
- Gas heat section inspected: burners, tubular heat exchangers, flame signal, venting and a combustion reading
- Controls verified against the schedule the building actually runs — thermostat or DDC setpoints, occupancy times, and lockouts that a tenant has quietly overridden
- Refrigerant circuit checked by superheat and subcooling, with any leak found and recorded rather than topped up
How Often, By Building Type
Free quotes, written pricing.
- Office and professional space: two full seasonal visits, quarterly filter and belt checks. Loads are steady and predictable
- Restaurant and food service: quarterly at minimum, and the makeup air unit gets its own attention. Grease-laden air and a hard-working exhaust hood put the building under negative pressure, which is why the front door pulls shut and why appliances can backdraft
- Retail: quarterly, with visits timed around trading hours. Door-open cycling in summer means the units run far more than their schedule suggests
- Warehouse and light industrial in Stoney Creek or along Burlington's North Service Road: two visits a year for unit heaters and destratification fans, more if the process generates dust or fumes
- Medical, dental and lab space: quarterly, with filtration and pressure relationships documented every visit
Compliance and Records That Matter in Ontario
Work on the gas train, burners and venting of a commercial appliance must be done by a TSSA-licensed technician working to CSA B149.1. Licence class matters here in a way it does not in a house: G2 carries an input ceiling that a large rooftop unit can exceed, while G1 does not. Ask which class is coming to your roof before the invoice arrives.
Refrigerant is the other file. Ontario's halocarbon rules require leaks to be repaired rather than tolerated, and require records of refrigerant added and recovered. A unit that gets topped up every spring is not being maintained; it is being documented as a leaking system, and that record follows the equipment. Electrical work needs ESA authorization, and roof access needs a fall-protection plan — a real one, since most commercial units sit within reach of an unguarded edge.
Planned Versus Reactive: What Actually Changes
- Timing: planned work happens on a Tuesday morning when the building is empty. Reactive work happens on the first 32°C afternoon, at after-hours rates, in front of your tenants or customers
- Parts: a belt, an actuator or a contactor is stock. A compressor or a control board on a discontinued unit is a lead-time problem that no rate premium shortens
- Scope: a seized damper linkage found in April is a linkage. Found in January after the coil has frozen and split, it is a coil
- Records: a maintenance file with dated visits supports warranty claims, satisfies an insurer after a water loss, and answers the first question a buyer's engineer asks during due diligence
- Budget: planned work is an operating line you can forecast. Reactive work is a capital surprise in the middle of a fiscal year
Verdict: How to Structure the Contract
Ask for a written scope per unit, not a flat "maintenance" line. It should name every rooftop unit and split system by tag and serial, list the tasks above with the visit frequency, include filters and belts as consumables rather than extras, and produce a report per visit with readings on it. Then hold the contractor to the report — a visit with no numbers on the sheet is a visit you cannot verify.
If you are running a mixed site, get clear on what you actually have first; the difference between an RTU and a split system explains why the two need different scopes and different visit lengths.
ZK Mechanical writes commercial HVAC maintenance agreements for offices, restaurants, retail and light industrial buildings across Burlington, Oakville, Hamilton and the wider GTA, and our maintenance plans cover the smaller mixed-use sites. Send us your unit list and we will scope it in writing.
Frequently asked questions
How often should commercial HVAC be serviced?
Two full seasonal visits is the floor for offices and warehouses, with filter and belt checks each quarter. Restaurants, retail and medical space earn quarterly full visits because their equipment runs longer hours under dirtier conditions. The right interval is set by run hours and air quality inside the building, not by the size of the unit.
What does a commercial HVAC maintenance visit include?
Filters and belts, motor and bearing condition, economiser damper travel and actuator function, condensate pan and trap, coil cleaning, curb and flashing inspection, a full gas heat section check with combustion readings, refrigerant circuit verification by superheat and subcooling, and control setpoints checked against the building's real occupancy schedule. Each visit should end with a written report carrying actual readings.
Why does my rooftop unit keep freezing the coil in winter?
The usual cause is an economiser damper stuck open, so the unit is pulling in outdoor air well below freezing while trying to heat or while the cooling circuit still cycles. Blocked filters and a failed outdoor-air sensor produce the same result. It is a scheduled-visit item: the linkage and actuator are checked and stroked, which takes minutes when someone is already on the roof.
Is a maintenance contract worth it for a small business?
It is if downtime costs you trading hours. Beyond the mechanical work, a contract buys scheduled visits outside business hours, a documented service file for warranty and insurance, and a contractor who already knows your equipment when something does fail. For a single small rooftop unit, two seasonal visits with filters included is usually the right size of agreement.