Rooftop HVAC Unit Maintenance: What Ottawa Building Managers Often Overlook

If you manage a commercial property in Ottawa, there’s a good chance you have one or more rooftop HVAC units keeping your tenants comfortable year-round. Rooftop units — commonly called RTUs — are workhorses. They’re out of sight, largely out of mind, and expected to just keep running.

That’s exactly the problem.

Because RTUs sit on the roof and aren’t part of daily foot traffic, they’re among the most under-maintained mechanical systems in commercial buildings. Ottawa’s climate makes this especially costly. Between January deep freezes, spring thaws, summer humidity, and fall debris season, your rooftop units face more stress per year than most equipment in the building.

Here’s what experienced building managers tend to miss — and what staying on top of it can save you.

1. Coil Cleaning Gets Skipped Far Too Long

Both the condenser coil (which releases heat outside) and the evaporator coil (which absorbs heat inside) need to be cleaned regularly. In Ottawa, cottonwood seed season in late spring is a particular culprit — those fluffy white fibres pack into condenser coils and choke airflow almost overnight.

A dirty coil forces the unit to work harder to achieve the same output. That translates directly into higher energy bills, more compressor wear, and a shorter equipment lifespan. Most manufacturers recommend coil cleaning at least twice a year. Many commercial properties in Ottawa go two or three years between cleanings without realizing the compounding cost.

What to watch for: A spike in energy consumption in late May or June with no corresponding change in occupancy or thermostat settings is often a dirty coil problem.

2. Drain Pans and Condensate Lines Are a Neglected Mess

During cooling season, your RTU removes significant moisture from the air. That water has to go somewhere — into a drain pan, through a condensate drain line, and out of the building. When those lines are partially blocked by algae, debris, or mineral buildup, water backs up into the pan. When the pan overflows, water finds the path of least resistance — which is usually into your roof membrane or down into the ceiling below.

In Ottawa’s commercial building stock, particularly older flat-roofed buildings in areas like Centretown or the ByWard Market, condensate-related water damage is one of the more common and entirely preventable maintenance headaches.

Drain pans and condensate lines should be flushed and inspected every spring before cooling season begins. It takes a technician 20 minutes. The alternative — a water-damaged ceiling, disrupted tenants, and potential mould remediation — takes considerably longer.

3. Economizer Dampers Fail in Ways Nobody Notices

Many commercial RTUs in Ottawa are equipped with economizers — dampers that allow the unit to bring in fresh outside air for “free cooling” when outdoor temperatures are appropriate. When an economizer is working correctly, it can meaningfully reduce cooling energy costs during Ottawa’s spring and fall shoulder seasons.

When an economizer damper fails — and they do fail, through a stuck actuator, a broken linkage, or a faulty sensor — one of two things happens:

The damper gets stuck open. In winter, this means your unit is pulling in -20°C air and your heating system is working overtime to compensate. Tenants complain it’s cold. Energy bills spike. Most managers assume it’s just a cold Ottawa winter.
The damper gets stuck closed. You lose the efficiency benefit entirely and may compromise indoor air quality without realizing it.

Economizer function should be physically verified — not just electronically checked — at every maintenance visit. This is an area where a quick visual inspection by a qualified technician catches problems that a building automation system won’t flag.

4. Rooftop Penetrations and Unit Curbs Are Ignored Until There’s a Leak

The HVAC unit itself sits on a curb — a raised frame that’s flashed and sealed into the roof membrane. Over time, Ottawa’s freeze-thaw cycles work on those seals. The metal curb expands and contracts. Flashing lifts. Caulking cracks.

Water doesn’t need a big gap to find its way in. A small breach in the curb flashing can quietly allow water infiltration for months before it becomes visible inside the building. By then, insulation is saturated and roof deck material may be compromised.

Inspecting the curb, flashing, and any roof penetrations associated with the HVAC unit should be part of every spring maintenance visit — ideally done in coordination between your HVAC contractor and your roofing contractor so nothing falls through the cracks between trades.

5. Filter Changes Are Happening on a Schedule, Not on Condition

Many building operators are on a quarterly or semi-annual filter change schedule. That’s a reasonable starting point, but it doesn’t account for what’s actually happening in your building. A rooftop unit serving a restaurant kitchen, a woodworking shop, or a high-traffic retail space will load up a filter much faster than one serving a quiet office floor.

A clogged filter restricts airflow across the evaporator coil. The coil gets too cold. In serious cases, it freezes — blocking airflow entirely and eventually causing the unit to shut down or the compressor to run hot. In milder cases, the unit just runs inefficiently for months while nobody notices.

Check filters by condition. In high-demand applications, monthly checks during peak season are appropriate. At minimum, your maintenance technician should be physically pulling and inspecting filters at every visit rather than just noting the date of the last change.

6. Refrigerant Levels Drift and the Problem Compounds Quietly

RTUs don’t consume refrigerant — if the charge is low, there’s a leak. A slow refrigerant leak in a commercial RTU can go undetected for a long time. The unit still runs. Cooling is just slightly less effective than it should be. Tenants maybe turn the thermostat down a little further. Energy use creeps up.

Meanwhile, a low refrigerant charge causes the compressor to work under conditions it wasn’t designed for. Compressors are the most expensive component in the unit. A refrigerant leak caught early costs a few hundred dollars in repair and recharge. A compressor replacement on a large commercial RTU can run several thousand.

Under current refrigerant regulations, commercial units above a certain charge size are required to be checked regularly for leaks. Many building operators don’t realize this falls under their compliance obligations, not just their maintenance preferences.

7. End-of-Life Planning Gets Kicked Down the Road

The average commercial rooftop unit has a service life of 15 to 20 years with good maintenance. Many Ottawa buildings are running units that are well past that mark. There’s a natural tendency to keep repairing rather than replacing — each individual repair seems cheaper than a capital replacement project.

The problem is that aging units become progressively less efficient, parts become harder to source, and the risk of a mid-season failure grows every year. A rooftop unit that fails in August during Ottawa’s peak heat or in January during a cold snap creates an emergency situation: expedited equipment costs, disrupted tenants, and whatever damage accumulates in the meantime.

A good commercial HVAC contractor will give you an honest equipment condition assessment and help you plan replacements on your timeline rather than the equipment’s timeline.

The Bottom Line for Ottawa Building Managers

Rooftop units are easy to neglect precisely because they work quietly and out of view. But in Ottawa’s climate — where equipment faces genuine extremes in both directions — deferred RTU maintenance has a way of becoming expensive in a hurry.

The good news is that most of the issues above are inexpensive to catch and correct when identified early. A proper commercial HVAC maintenance agreement that includes roof access, physical equipment inspection, and documentation gives you visibility into the condition of your equipment before it becomes a problem.

If your rooftop units haven’t had a thorough inspection recently — or if you’re not sure what the last service report actually covered — it’s worth getting a second set of eyes on them before the season changes.