01Measure the pattern before changing settings
Measure air temperature at multiple points across the outlet plane after the process reaches a stable condition. Record the fan speed, airflow, heater stages, inlet temperature and sensor readings at the same time. A single probe near one wall cannot show whether the full cross-section is uniform.
Compare the measured pattern with the duct layout and heater orientation. A persistent hot stripe or cold corner often points to a flow-distribution problem rather than insufficient total heater power.
02Check the airflow first
- Dirty filters, closed dampers or a fan operating away from its design point
- Elbows, transitions or tees too close to the heater face
- Uneven velocity caused by upstream obstructions or poor duct geometry
- Element banks with bypass gaps or blocked passages
- Air leakage that changes flow distribution or recirculation
Confirm the fan can deliver the required airflow at the system pressure drop. A heater may increase resistance enough to reduce flow or distort the velocity profile. Correcting upstream mixing or adding a properly designed transition can help, but the solution depends on available straight length and duct geometry.
03Review element layout and control stages
Check that element rows are distributed across the active duct area and that each bank is wired and energized as designed. A failed element group can create a cold band even when the control display shows a heating demand. Measure phase currents and verify stage operation using safe site procedures.
If the heater is split into stages, abrupt staging at low airflow can create local temperature swings. Modulating control may improve stability when properly sized, but it cannot correct a badly uneven velocity profile.
04Place sensors where they represent the process
A control sensor placed too close to the element face may see radiant or local hot air and shut stages down early. A probe near a duct wall may miss the core flow. Locate the control sensor where it measures mixed process air, and use an independent high-limit sensor near the heater outlet where it can detect abnormal local temperature.
Check probe insertion depth, orientation, calibration, response time and wiring. If uniformity is critical, specify an allowable cross-sectional temperature spread and the measurement method during commissioning.