Electric duct heaters provide precision reheat and primary space heating in commercial HVAC systems, cleanrooms, and pharmaceutical facilities. Because they operate directly inside air distribution ductwork, incorrect installation creates serious hazards — from scorched duct insulation to tripped thermal cutouts and premature element burnout.
Follow this 6-step installation guide developed by our HVAC heating engineers at Global Industrial Heaters.
Step 1: Check Duct Dimensions and Velocity Profile
Before cutting duct openings, ensure the duct velocity meets the manufacturer's minimum requirement (typically at least 1.5 to 2.5 meters/second or 300–500 FPM). If air velocity falls below this threshold, finned elements overheat rapidly.
Step 2: Maintain Necessary Clearances
Avoid placing duct heaters directly adjacent to fan discharge transitions, dampers, or sharp 90-degree duct elbows where airflow creates turbulent dead-zones. Maintain a straight duct length of at least 1.5 duct diameters upstream and downstream.
Step 3: Mechanical Insertion & Gasketing
Slide the heater frame into the duct cut-out. Ensure the terminal enclosure remains outside the duct in an accessible location with at least 600mm service clearance. Use high-temperature silicone gasketing between the heater mounting flange and duct sheet metal to prevent conditioned air leakage.
Step 4: Airflow Interlock Wiring (Crucial Safety)
Never energize a duct heater without positive airflow verification. Wire a differential air pressure switch across the heater section, connected in series with the main contactor holding coil. If the AHU blower belt slips or the fan shuts down, the heater must de-energize instantly.
Step 5: Dual Thermal Cutout Protection
Every Global Industrial Heaters duct heater includes two built-in thermal safety devices:
- Automatic Reset High-Limit Cutout: Opens the control circuit automatically during low-airflow events, resetting once normal air circulation is restored.
- Manual Reset Thermal Cutoff: Secondary fail-safe cutout that disconnects power if primary limits are breached, requiring technician inspection before re-arming.
Step 6: Pre-Power Insulation Checks
Before applying 415V 3-phase power, test each phase against ground using a 500V DC insulation tester (Megger). Insulation resistance must exceed 50 MΩ. Turn on the AHU blower first, confirm steady airflow, and then energize stage 1 heating.