Rooftop HVAC Units: What Neglect Actually Costs
RTUs are out of sight and they stay that way until the tenants complain. What a real quarterly service covers and the failures that come from skipping it.
By Derek Mills, Co-owner, service lead ·
Nobody goes on the roof. That is the whole problem with rooftop units.
A furnace in a basement gets noticed. Somebody walks past it, hears it, sees a puddle. An RTU sits on a flat roof behind a parapet, and the first anybody knows about a problem is a call from a tenant saying the space is 82 degrees.
Why they fail early
Weather, constantly. They live outside through everything we get. Panels back out, gaskets dry and crack, and water finds its way into places that were sealed when it was installed.
Belts. Most RTUs still use belt drive blowers. Belts stretch, glaze, and crack. A stretched belt slips, and a slipping belt moves less air, which means less capacity while everything looks like it is running. Cheap part, quick change, and it is the single most common thing we replace.
Coils pack with debris. Condenser coils on a roof collect cottonwood, dust, and whatever the neighboring exhaust fan is putting out. A restaurant hood dumping grease into the air near an RTU coil is a special case and those coils need chemical cleaning, not a rinse.
A dirty condenser coil raises head pressure. High head pressure raises amp draw, raises operating cost, and shortens compressor life. It is a slow expensive failure that looks like nothing until the compressor goes.
Condensate drains and pans. Plugged drains overflow. On a rooftop unit that water goes into the curb, into the duct, or through the roof deck. Water damage from a plugged three dollar drain is a bad way to spend money.
Economizers. If your unit has one, there is a good chance it does not work. The linkage seizes, the actuator fails, the sensor drifts. A stuck economizer either brings in outdoor air when it should not, which spikes your heating and cooling load, or refuses free cooling on a 55 degree day when the building could be cooling for the cost of running a fan. This one is worth checking specifically because a broken economizer is invisible and expensive.
Curb and duct seals. Gaps at the curb leak conditioned air into the roof cavity and pull unconditioned air in.
What a real PM visit covers
Quarterly is the usual cadence for commercial equipment, with heavier work in spring and fall.
- Filters, on a schedule matched to the environment, not the calendar alone
- Belt condition and tension, and spare belts left on site
- Bearings lubricated where applicable
- Condenser and evaporator coils inspected and cleaned as needed
- Condensate pan and drain cleared, trap verified
- Amp draw on compressors and motors compared against nameplate
- Refrigerant charge verified by superheat or subcooling
- Contactors inspected for pitting, capacitors tested against rating
- Economizer operation actually exercised and verified, not just glanced at
- Heat section: burners, ignition, flame sensing, heat exchanger inspection
- Safety controls tested
- Cabinet panels, gaskets, and curb seal checked
- Roof around the unit checked for standing water and damage
Ask for a written report with measured values. Amp draws, temperature splits, pressures. A report with numbers lets you see a trend developing across visits, which is how you replace a capacitor on a Tuesday instead of a compressor on a Saturday in July.
What the failures cost
A belt is a small part. A compressor is not. A roof leak that soaks insulation and drops ceiling tile is not either, and neither is a day of a retail space being unusable.
The pattern I see is that deferred maintenance does not save money, it moves it. It moves the spend from small scheduled amounts to large unscheduled ones, and it moves the timing from when it is convenient to when it is worst.
Access matters more than people think
If there is no safe permanent way onto the roof, service costs more and takes longer every single visit, and some work simply will not happen. If you are building or renovating, a proper roof hatch and a walkway pad to the units pays for itself over the life of the equipment.
Same for clearance. Units crammed against a parapet or against each other cannot be serviced properly, and they cannot get the airflow they need either.
If yours have been neglected
Start with an assessment rather than a plan. We go up, look at every unit, and give you a written condition report with what is urgent, what is coming, and what can wait. Then you can budget rather than react.
Sometimes the honest answer is that a twenty year old unit is not worth a major repair and should be scheduled for replacement in the off season, on your timeline, rather than emergency replaced in August.