If one side of a commercial building is hot while another is cold, the HVAC system is not delivering the right airflow, cooling capacity, or control to every zone. In Northern New Jersey summers that usually traces back to failing rooftop units, blocked ducts or VAV boxes, bad sensors, or a building automation schedule that is fighting the actual occupancy. It is rarely "just the thermostat."
Uneven Temperatures Are a System Problem
Commercial buildings are zoned for a reason. Different exposures, floor plates, and occupancy patterns need different cooling. When one conference room freezes and the west offices bake, something in that balance has failed.
Common causes:
- One rooftop unit or zone is down while others are still cooling
- Dirty filters, dirty coils, or failing fans cutting airflow to part of the building
- VAV boxes stuck open or closed
- Dampers not responding
- Thermostats or sensors in the wrong place, or drifted out of calibration
- Sun load on glass exposures the system no longer has capacity to handle
- After-hours or weekend setbacks that recover unevenly on Monday morning
What Facility Managers Should Check First
Before assuming you need a full redesign, narrow it down. Which floors or exposures are affected? Did it start suddenly or get worse over weeks? Are supply vents blowing air in the hot areas? Have filters been changed? Are BAS alarms showing a specific unit offline?
A sudden hot wing often means a failed RTU, breaker, or controls issue. A chronic hot-and-cold pattern often means airflow, zoning, or capacity problems that need a technician with the building's drawings and trend data.
Why Summer Makes It Worse
Peak summer load exposes weak zones. A unit that "mostly keeps up" in May cannot hold the west exposure in July. Economizers stuck in the wrong position, low refrigerant, or failing compressors show up first as uneven comfort, then as full no-cooling calls.
Multi-tenant offices feel this fast because tenants compare spaces. One suite at 72 and the next at 79 becomes a management problem, not just a mechanical one.
What a Proper Diagnosis Should Include
A commercial tech should identify which equipment serves the problem area, measure supply temperatures and airflow where needed, inspect filters and coils, check zone controls, and verify sensor accuracy. On BAS buildings, trend logs often show the failure clearer than a single walkthrough.
Throwing portable AC units at the symptom can buy time. It does not fix the zone.
FAQ
Can one bad thermostat cause a whole wing to run hot? Yes, if that sensor is what the zone or RTU is trusting. A thermostat on a sunny wall or above equipment will lie to the system.
Is this always an airflow problem? No. It can be capacity, controls, a failed unit, or outdoor-air issues. Airflow is one of the first things to check, not the only one.
Why does the problem show up only in the afternoon? West-facing glass and peak outdoor temperatures stack the load later in the day. Weak zones fail there first.
Should we rebalance the whole building? Sometimes. First confirm equipment is actually working. Rebalancing a failed unit wastes money.
Can KCG diagnose uneven commercial cooling? Yes. KCG services commercial HVAC across Northern and Central New Jersey and can inspect units, zoning, and controls. Call 973-335-3884.
KCG Energy Management is a veteran-owned commercial HVAC contractor based in Moonachie, NJ. NJ HVAC License #19HC00737600. If part of your building is hot while the rest is fine, we can find whether it is equipment, airflow, or controls before another heat wave makes it louder.