Rooftop units need regular filter changes, seasonal checks of the heating and cooling sections, and attention to the parts that quietly fail, such as economizer dampers and condensate drains. A simple maintenance routine, done consistently, keeps them running efficiently and catches safety problems like cracked heat exchangers before they become serious.
Packaged rooftop units, often called RTUs, combine fans, filters, heating, cooling and outdoor air control in one cabinet. They sit outside in Canadian weather all year, which is hard on them. Because they are out of sight, problems can go unnoticed until tenants complain or the unit stops.
What a rooftop unit contains
- Supply fan and motor, often belt-driven, that pushes air through the ducts.
- Filters on the return and outdoor air before the coils.
- Gas heating section with burners, heat exchanger, inducer fan and flue, or an electric heating section.
- Refrigeration circuit with compressor, condenser coil and fans, and an evaporator coil inside the cabinet.
- Economizer with outdoor, return and relief dampers that use cool outdoor air for free cooling when conditions allow.
- Condensate drain and trap that carry away water from the cooling coil.
- Controls: thermostat or building automation connection, safeties and the unit's own control board.
A practical maintenance routine
Intervals depend on the manufacturer's instructions, how dusty the location is and how many hours the unit runs. The routine below is a general starting point.
Every visit (often monthly or quarterly)
- Check and change filters. Make sure they fit the rack with no gaps for air to bypass.
- Check belts for wear, cracking and tension, and look at pulley alignment.
- Listen for unusual fan or motor noise and check for vibration.
- Look for water, oil or refrigerant stains around the unit.
- Make sure access panels are closed and secured.
Before the cooling season
- Clean condenser and evaporator coils.
- Clear and flush the condensate drain and trap, and check the drain pan for rust.
- Have a qualified technician check refrigerant operation and electrical connections.
- Test the economizer: dampers should move freely and respond to the controls.
Before the heating season
- Have a licensed gas technician inspect the burners, ignition, flame sensor and safety controls.
- Inspect the heat exchanger for cracks, corrosion or holes.
- Check the flue and inducer fan, and confirm the venting is clear.
- Confirm the outdoor air damper closes to its minimum position and does not freeze open.
Heat exchangers and carbon monoxide. A cracked or corroded heat exchanger can let combustion products into the supply air. Have gas-fired units inspected by a licensed gas technician before each heating season, and make sure the spaces they serve have working carbon monoxide detection where required.
The economizer: the part most often broken
Economizers can save a great deal of cooling energy by using outdoor air when it is cool enough, which is much of the year in most of Canada. They are also among the most frequently failed parts of a rooftop unit. Seized linkages, failed actuators, unplugged sensors and dampers wired shut are all common. A broken economizer may stick closed, wasting energy and starving the space of fresh air, or stick open, letting cold air freeze coils in winter. Ask your service contractor to test it as part of every spring visit.
Roof conditions matter too
The unit's curb and the roof around it are part of the system. Check that curb flashing is intact, that there is no ponding around the unit and that service paths do not damage the roof membrane. Make sure there is safe access to the roof and safe working distance from roof edges. Our guide to roof drains and ponding water covers drainage issues around equipment.
Keeping records
Give each unit a clear identifier on the roof and in your records. Log filter changes, service visits, repairs and refrigerant work. Over time, this history shows which units are costing the most to keep running and helps you plan replacements rather than react to failures.
A typical maintenance visit, step by step
A good contractor's spring visit follows a predictable order, and knowing it helps you check what you are paying for. For each unit, the technician should record what they found as well as what they did:
- Before opening the unit: note the unit identifier, any alarms on the controls, and whether the unit is running and why. Isolate power following lockout procedures before working inside.
- Filters and belts: record the filter size, type and condition, replace as needed, and note belt condition and tension.
- Coils and drains: record coil condition before cleaning. Flush the drain and confirm water flows freely from the trap.
- Economizer: with power restored, command the dampers open and closed and record whether they follow. Note the minimum outdoor air position.
- Cooling start-up: record operating pressures or temperatures as the technician's practice requires, and any refrigerant added. Refrigerant work must be logged under the rules in your province.
- Wrap-up: list deficiencies found but not fixed, with a recommendation for each.
If your service reports only say "PM completed" with no readings or deficiencies, ask for more. Readings recorded each season are what let you spot a unit that is slowly losing performance.
Common mistakes
- Filters bought by the case in one size and forced into racks they do not fit.
- Condensate traps missing or dry, so the drain pan overflows into the ceiling below.
- Economizer dampers disconnected after a freeze problem and never repaired.
- Units left without identifiers, so service reports cannot be matched to equipment.
When to repair and when to replace
There is no fixed age at which a rooftop unit should be replaced. Consider replacement when major components such as the compressor or heat exchanger fail on an older unit, when repair costs keep rising, when parts or refrigerant become hard to get, or when the unit no longer suits the space it serves. Replacing a unit is also a chance to reconsider its size, efficiency and whether a heat pump would suit the building.
How ehZee can help
As part of our mechanical system inspections, we inspect rooftop units, review service records and give you a ranked list of findings across all your units. That makes it easier to plan maintenance and replacements, and to check that your service contractor is covering what matters.
Common questions
How often should rooftop unit filters be changed?
It depends on the filter type, how dusty the area is and how long the unit runs. Many buildings change them quarterly, with more frequent changes in dusty locations or during construction. Checking pressure drop across the filter is a more reliable guide than the calendar.
Can our maintenance staff do this work?
Building staff can usually change filters and belts and keep drains clear, if they are trained and can access the roof safely. Gas, refrigerant and electrical work must be done by licensed technicians.
Why does our rooftop unit short cycle?
Common causes include an oversized unit, a thermostat in the wrong place, dirty filters or coils, or a safety control tripping. A technician should diagnose it, since short cycling wears equipment out faster.
What is the drain trap for?
The cooling coil sits in a section of the unit under suction from the fan. Without a correctly sized trap, air can be pulled back through the drain and water cannot leave the pan, which leads to overflow into the unit or the ceiling below. The trap also needs to be kept from freezing in winter.