If your Hamilton business runs on a rooftop unit, what happens up on that roof directly affects your energy bills, your indoor comfort, and your ability to stay open. This guide covers everything you need to know about commercial RTUs: what they are, how they work, what installation involves, how to maintain them, and how to decide when it’s time to repair or replace.

What Is a Commercial Rooftop Unit (RTU)?

A rooftop unit, or RTU, is a self-contained HVAC system installed on the roof of a commercial building. Everything is housed in a single cabinet: the compressor, evaporator coil, condenser coil, blower fan, heating elements, and controls. The unit connects directly to your building’s ductwork and conditions air for the entire space or for individual zones.

RTUs are the most common commercial heating and cooling solution in Hamilton and across Ontario. Restaurants, retail plazas, offices, warehouses, and light industrial facilities all rely on them.

RTU vs. Split System: What’s the Difference?

A traditional split system separates the cooling components (outdoor condenser) from the heating components (indoor air handler or furnace). With an RTU, everything is packaged together on the roof. That design keeps all the mechanical equipment out of your usable interior space, simplifies maintenance access, and generally streamlines installation. The trade-off is that rooftop units are exposed to Hamilton’s weather year-round, which is exactly why regular service matters more for RTUs than it does for indoor equipment.

Why Hamilton Businesses Choose RTUs

Hamilton’s commercial buildings range from century-old warehouses near the waterfront to newer retail strips and industrial parks on the east and west mountain. Most have something in common: flat or low-slope roofs with existing RTU infrastructure already in place.

RTUs are well-matched to this climate. A properly maintained unit handles both the heating load on a January morning when temperatures drop to -15°C and the cooling load on a humid August afternoon. You don’t need separate systems. For businesses that can’t afford HVAC downtime, that reliability is what makes RTUs the default choice.

The other practical reason is space. No mechanical room, no indoor unit consuming square footage, no refrigerant lines running through occupied areas. Everything that makes noise and generates heat stays on the roof.

Our commercial HVAC services in Hamilton cover installation, maintenance, and repair for RTUs across all commercial sectors.

Make-Up Air Units for Hamilton Restaurants

Restaurants are a special case. Commercial kitchen hoods exhaust large volumes of air continuously to remove smoke, grease, and heat. That air has to be replaced, and a standard RTU is not designed for this job. Standard units recirculate a mix of indoor and outdoor air. They don’t supply enough fresh outdoor air to keep a kitchen properly pressurized.

That’s where make-up air units (MAUs) come in. An MAU is a specialized rooftop unit that draws in 100% outdoor air, conditions it, and delivers it to the kitchen to replace what the hoods are exhausting. Fox handles commercial refrigeration and make-up air for restaurant and food service clients across Hamilton. If you’re planning a new kitchen buildout or replacing aging exhaust equipment, loop us in early. Getting the right unit specified before construction starts saves significant money compared to correcting it after the fact.

How a Rooftop Unit Works

An RTU draws air in, conditions it, and pushes it through your ductwork. Here’s what’s happening inside the cabinet:

• Compressor: Circulates refrigerant through the cooling cycle.
• Evaporator coil: Absorbs heat from the air passing through it during cooling mode.
• Condenser coil: Releases that heat outside.
• Blower fan: Moves conditioned air through your ductwork and into the building.
• Heat exchanger or heating elements: In heating mode, a gas burner or electric resistance coil warms the air before it’s distributed.
• Air filters: Remove dust and particulates before air reaches the interior.
• Economizer (on many units): A damper system that pulls in cool outdoor air for “free cooling” when outside temperatures are low enough, reducing compressor load and cutting energy costs.

The cycle loops continuously: the blower pulls return air back from your space, mixes it with a percentage of fresh outdoor air, conditions it, and pushes it back through your supply ducts.

Heating Mode vs. Cooling Mode in Ontario’s Climate

In Hamilton, an RTU has to work hard in both directions. Heating mode typically runs from November through April. The unit fires the gas burner or heating elements to warm incoming air before distributing it through the building. Cooling mode takes over in May and runs through September, when the refrigerant cycle handles heat removal.

Hamilton’s shoulder seasons, October and early May, often require both modes within the same week. Modern RTUs handle this automatically based on thermostat settings and outdoor temperatures.

One thing that catches building owners off guard: units with economizers can provide free cooling on cool spring days without running the compressor at all. If your unit’s economizer isn’t functioning correctly, you’re paying for mechanical cooling you don’t need. This is one of the items we check during every service visit.

RTU Installation in Hamilton: What to Expect

Installing a commercial rooftop unit involves more than setting a unit on a roof. A proper installation starts with planning and ends with a full commissioning test. Every step matters for how the unit performs over its 15 to 20 year lifespan.

Here’s how the process typically goes:

1. Site assessment and load calculation. Before any equipment is ordered, we evaluate the building’s heating and cooling load: square footage, occupancy, insulation, window area, ventilation requirements, and how the space is used. A restaurant and an office of the same square footage have very different load profiles. Getting this step right determines everything else.
2. Equipment selection. RTUs are available in a wide range of configurations: gas/electric, heat pump, economizer-equipped, multi-zone, and more. We select the unit based on the load calculation, not whatever is available at the distributor. Oversizing and undersizing both cause problems (see sizing section below).
3. Roof preparation. The RTU mounts on a curb that raises it above the roof surface and connects it to the ductwork below. On a replacement job, we inspect the existing curb for deterioration and replace it if needed. On a new installation, everything is built to current Ontario Building Code standards.
4. Crane placement. Commercial RTUs are heavy. Depending on the unit size and building height, a crane is required to lift the equipment into position. We coordinate this with you to minimize disruption to operations.
5. Electrical and gas connections. All wiring and gas piping must meet the Ontario Electrical Code and TSSA requirements. This is not a step to cut corners on.
6. Commissioning. Once the unit is set, we verify gas pressures, refrigerant charge, airflow balance, thermostat calibration, and economizer function before the job is considered complete.

How to Size an RTU for Your Building

Rooftop units are sized in tons of cooling capacity, typically ranging from 3 to 25 tons for most Hamilton commercial buildings. Larger industrial facilities may require multiple units or custom configurations.

Sizing matters more than most people realize. An undersized unit runs constantly and never reaches the setpoint. An oversized unit short-cycles: it turns on, meets the temperature quickly, shuts off, and repeats. Short-cycling wears out components faster and leaves the space feeling clammy because the unit doesn’t run long enough to dehumidify properly.

We don’t estimate. Every installation starts with a proper load calculation, and we’ll explain what we found and why we’re recommending a specific unit. Call 905-387-2403 to schedule a free site assessment.

RTU Maintenance: How Often and What’s Covered

Most commercial buildings in Hamilton should have their RTU serviced at minimum twice a year: once in spring before the cooling season starts and once in fall before heating season. Restaurants and any facility running 16 or more hours a day are better served by quarterly visits.

A professional RTU tune-up covers:

• Filter inspection and replacement
• Evaporator and condenser coil cleaning
• Blower motor and belt inspection
• Refrigerant pressure check
• Electrical connection tightening
• Economizer and damper function test
• Gas pressure verification (fall service)
• Thermostat and controls check
• General inspection for leaks, corrosion, and wear

Most service visits on a standard unit take two to three hours. This is what keeps an RTU running for 15 to 20 years rather than 8 to 10.

Our VIP Maintenance Program is built for commercial clients who want consistent service without having to schedule it themselves. We track your service history, contact you when a visit is due, and show up on time.

The Risk of Out-of-Sight, Out-of-Mind Maintenance

RTU equipment gets neglected more than indoor equipment does. It’s on the roof. Nobody walks past it. Nobody hears it struggling from inside the building until something breaks.

That neglect has real costs. Coils clogged with a season’s worth of dirt force the compressor to work harder, increasing energy consumption by 15 to 25%. A loose belt can cause a blower failure mid-January. Low refrigerant doesn’t just reduce cooling performance: it can overheat the compressor and cause it to fail, turning a $300 refrigerant top-off into a $5,000 compressor replacement.

RTU Repair in Hamilton: Signs You Should Call a Pro

Most RTU problems give warning before they become emergencies. Watch for these:

• Rising energy bills without a clear cause. A 15 to 20% increase in heating or cooling costs often points to a dirty coil, refrigerant leak, or failing economizer.
• Uneven temperatures across zones. If one part of your building is comfortable and another isn’t, the cause could be a failing zone damper, a ductwork problem, or a unit that’s lost capacity.
• Short cycling. The unit turns on, runs briefly, and shuts off repeatedly. Common causes include refrigerant issues, a faulty thermostat, or an oversized unit that was never properly sized.
• Unusual noises. Banging, rattling, or grinding usually means a loose component or a failing motor bearing.
• Ice forming on the unit. Ice on the evaporator coil points to low refrigerant or restricted airflow. Running the unit in this condition damages the compressor.
• Poor indoor air quality. If the building feels stuffy or excessively humid even when the RTU is running, the filters, coils, or economizer likely need attention.

Fox provides 24/7 emergency service for commercial clients in Hamilton. If your rooftop unit fails in the middle of February, we’re available. Call 905-387-2403.

Repair or Replace? How to Decide

The general benchmark: if a repair costs more than 30 to 40% of what a full replacement would cost, and the unit is already 12 to 15 years old, replacement is usually the better financial decision. You’re spending a significant amount to extend the life of aging equipment that will likely need another major repair within a few years.

Other factors that push toward replacement:

• The unit uses R-22 refrigerant, which was phased out. Replacement parts are scarce and expensive.
• Efficiency has been declining consistently even after regular service.
• The unit no longer meets the building’s load requirements, possibly because the space or its occupancy has changed.
• A renovation or buildout is already planned that would require ductwork changes anyway.

If you’re unsure which direction makes sense, we’ll give you a straight answer. Sometimes a repair is the right call. We’ll tell you when it is and when it isn’t.

Ontario Rebates for High-Efficiency RTU Upgrades

Ontario businesses upgrading to high-efficiency rooftop units may qualify for incentives through SaveOnEnergy.ca, the province’s energy efficiency program administered by the Independent Electricity System Operator (IESO). The program offers financial support for commercial and industrial customers who improve energy efficiency, including HVAC equipment upgrades.

Eligibility depends on your current equipment, the replacement unit’s efficiency rating, and your facility type. Program terms and rebate amounts change periodically, so we don’t publish specific figures here. The practical approach is to get a firm quote on the replacement equipment first, then check current program availability before committing.

Fox can help you assess which equipment qualifies and provide documentation for your application. If there’s money available for an upgrade you’re already planning, we’ll make sure you don’t leave it on the table.

Why Hamilton Businesses Have Trusted Fox Since 1938

Fox Refrigeration has been operating in Hamilton for 88 years. We’re a third-generation family business, and we’re still family-owned.

The “R” in Fox HVAC+R stands for refrigeration. It’s not a side service added to pad a service menu. It’s where the company started and it remains one of our core specialties. We service walk-in coolers and freezers, make-up air units, commercial refrigeration equipment, and rooftop HVAC systems for restaurants, retail operations, offices, and industrial facilities across Hamilton and the surrounding area.

When you call Fox, you’re talking to technicians who know Hamilton’s commercial building stock, who have worked on RTUs from the 1980s and units installed last year, and who aren’t going to recommend a replacement when a repair will do.

For service on your rooftop unit or to discuss a new installation, call 905-387-2403 or reach us at info@foxhvacr.com. We’re available 24/7 for commercial emergencies.

Frequently Asked Questions: Rooftop HVAC Units in Hamilton

What does RTU stand for in HVAC?

RTU stands for Rooftop Unit. It’s a self-contained HVAC system with the compressor, coils, blower, filters, and heating elements all housed in one cabinet, mounted on the roof of a commercial building. The unit connects to the building’s ductwork and conditions air for the entire space or for individual zones.

How often should a commercial RTU be serviced in Hamilton?

Most commercial buildings in Hamilton should have their RTU serviced twice a year: once in spring before the cooling season and once in fall before heating season. High-use facilities like restaurants or buildings running 16-plus hours a day benefit from quarterly inspections. Hamilton’s winters are hard on heating components, and skipping fall service is one of the most common causes of mid-winter RTU failures.

How long does a rooftop HVAC unit last?

A properly maintained RTU typically lasts 15 to 20 years. Units that miss regular service often fail at 8 to 12 years. When repair costs start approaching 30 to 40% of replacement cost, or when the unit is 15-plus years old and losing efficiency, replacement is usually the better investment, especially given the high-efficiency rebates available to Ontario businesses.

What is the difference between an RTU and a make-up air unit?

A standard RTU recirculates and conditions a mix of indoor and outdoor air. A make-up air unit (MAU) uses 100% fresh outdoor air with no recirculation. MAUs are common in restaurant kitchens where commercial hood exhaust constantly removes air from the space and the unit must continuously replace it. Both systems are installed on the roof and maintained similarly, but MAUs require additional insulation and energy to condition all-fresh outdoor air.

Are there rebates for upgrading to a high-efficiency RTU in Ontario?

Yes. Ontario businesses may qualify for energy efficiency incentives through SaveOnEnergy.ca when upgrading to a high-efficiency rooftop unit. Eligibility depends on the current system, the replacement unit’s efficiency ratings, and facility type. Fox Refrigeration can assess your building and help identify programs you qualify for before you commit to a replacement.