Why Your Commercial AC Struggles During a GTA Heatwave (And How to Prevent It)

A commercial rooftop unit (RTU) keeping a GTA building cool through the summer heat.

When Toronto hits 35°C with humidex pushing past 45, the calls start flooding in. Tenants complaining about warm offices. Restaurant kitchens turning into saunas.

Retail spaces losing customers who walk out the door looking for somewhere cooler. If your commercial AC has ever "died" during a heatwave, here's the uncomfortable truth: it usually didn't die. It hit its limit — a limit that was set months earlier by what you did (or didn't) do.

Here's why GTA heatwaves expose HVAC weaknesses, and what separates the buildings that sail through from the ones that cook.

Your System Was Designed for a Cooler Day Than You Think

Commercial cooling systems are sized around an industry benchmark called the ASHRAE design temperature. For the Toronto area, that figure is roughly 29°C — meaning equipment is engineered to keep your building comfortable in conditions that get exceeded only about 1% of summer hours.

That's the catch. GTA summers increasingly deliver stretches of 35°C+ days, back to back, with humidex climbing far higher and overnight temperatures that never drop enough for buildings to recover. When the mercury sits well above what your equipment was designed to handle, your rooftop units (RTUs) run continuously without their usual nighttime break. A system operating at 100% capacity for 14 hours straight behaves very differently than one cycling on and off — and small inefficiencies that go unnoticed in May become critical failures in July.

What Causes Commercial AC Heatwave Failures

1. Dirty condenser coils. This is the number one culprit. Your condenser coil sheds heat to the outside air. When it's caked with cottonwood seed, dust, and GTA pollution, it can't reject heat efficiently. On a mild day, you'd never notice. On a 36°C day, the system can't keep up, head pressure spikes, and the unit trips on a high-pressure safety lockout. The fix costs a fraction of an emergency call — but only if it's done before the heat arrives.

2. Low refrigerant charge. A slow leak that's been quietly building all spring won't show symptoms until the system is under maximum load. During a heatwave, an undercharged unit simply can't produce enough cooling, and you'll watch indoor temperatures climb even though the system is "running."

3. Aging capacitors and contactors. Heat is brutal on electrical components. Capacitors that are marginal in spring fail in extreme heat, leaving compressors and fans unable to start. This is one of the most common heatwave breakdowns — and one of the cheapest to prevent with a quick electrical check.

4. Restricted or neglected airflow. Clogged filters, closed dampers, and failing belts restrict airflow. Less air across the coil means less cooling delivered and a higher risk of the coil freezing over — which shuts cooling down entirely.

5. No staging or controls strategy. Buildings with multiple units that all slam on at once during peak heat can overwhelm electrical capacity and cause nuisance trips. Proper controls and staging keep load manageable.

Why "We'll Fix It When It Breaks" Costs You More

During a GTA heatwave, every commercial HVAC company in the region is buried. Response times stretch from hours to days. Emergency rates apply. Parts that are normally in stock get back-ordered because every building in the city needs the same capacitor or contactor at the same time.

Meanwhile, you're absorbing the real costs: tenant complaints (and potential lease disputes over comfort obligations), lost revenue in customer-facing businesses, spoiled inventory in food service, and reputational damage that lingers after the temperature drops. A single day of downtime during peak season often costs more than a year of preventive maintenance.

The Prevention Playbook

The good news: heatwave failures are among the most predictable — and preventable — problems in commercial HVAC. A proper spring or early-summer service should include:

• Condenser and evaporator coil cleaning

• Refrigerant charge verification and leak inspection

• Electrical component testing (capacitors, contactors, wiring connections)

• Filter replacement and airflow check

• Belt and motor inspection

• Controls and thermostat calibration

• Verification that safety lockouts and staging work correctly

Done before the heat arrives, this catches the marginal components that would otherwise fail at the worst possible moment.

Don't Wait for the Forecast

The buildings that get through a heatwave comfortably aren't lucky — they're prepared.

By the time Environment Canada issues a heat warning, the window to prevent problems has already closed.

If your commercial system hasn't had a thorough cooling-season service yet this year, now is the time. Burban Air Systems Ltd. provides preventive maintenance and emergency service for commercial buildings across the Greater Toronto Area. Get ahead of the next heatwave — contact us to schedule an inspection before your system is put to the test.