Slip-In Electric Duct Heaters

Slip-In Electric Duct Heaters | Industrial HVAC Heating

Slip-in electric duct heaters are designed for simple, flexible installation inside ductwork, making them a popular choice for both new construction and retrofit applications in commercial and industrial HVAC systems. The heater inserts directly into a rectangular opening cut in the side of the duct and is secured externally (typically with sheet metal screws), eliminating the need for a bolted perimeter flange connection.

This design allows the duct system to be fully installed before the heaters arrive, simplifies field modifications or replacements, and is especially convenient for retrofits into existing ducts where cutting a precise opening is easier than matching flanges.

What “Slip-In” Means A slip-in duct heater features a frame (except for the protruding terminal box) that slides into the duct through a cutout, with clearance around the inside edges for easy insertion. The heater is then fastened from the outside, creating a secure seal without requiring duct flanges to match the heater.

Provides straightforward installation and removal
Ideal for retrofits, existing duct systems, or when ductwork is already in place
Preferred for ducts up to about 4 feet wide (larger units may need internal supports)
Slip-in refers only to the mounting style, not the heating method (typically open coil elements)

Slip-In vs. Flanged Slip-in heaters insert into a cut opening in the duct side and are secured externally—making them easier for retrofits, field changes, or when exact flange matching isn't required. Flanged heaters bolt to matching duct flanges for a more rigid, permanent integration and are often chosen for new engineered systems or direct replacements of existing flanged units. When replacing a heater, matching the original mounting style (slip-in or flanged) is critical for proper fit.

Available Configurations NorthStock offers cataloged standard models like the Warren SL Series and Markel PD Series as well as custom Warren CBK Series (click here to request a custom CBK-Series quote) slip-in electric duct heaters tailored to your exact needs:

Wide range of kW capacities
Standard voltages: 208V, 240V, 480V (others available)
Single-phase and three-phase options
Custom duct sizes and insertion dimensions
Suitable for ducts with up to 1" interior insulation (extended terminals and cutout design support this)
Heaters are configured to match your application, airflow requirements, or existing setup.

Slip-In Electric Duct Heater Applications

Commercial and industrial HVAC systems
Retrofits and replacements in existing ductwork
Make-up air units, air handlers, VAV systems, and fan coil units
Process air heating and ventilation where easy installation or future access is important

Frequently Asked Questions (FAQ) – Slip-In Electric Duct Heaters

How are slip-in electric duct heaters installed? Cut a rectangular opening in the duct side, sized about 1/4" larger than the heater element section's height and width. Slide the heater frame into the opening (protect electrical components from metal debris during cutting), then secure externally with sheet metal screws through the terminal/control box flange. For insulated ducts (up to 1" interior insulation), units feature extended terminals. Ensure uniform airflow, correct orientation (usually horizontal; check labels for vertical), and adherence to codes (NEC, ASHRAE, NFPA 90A). Professional HVAC technician selection and installation is required.

Can these heaters be used for replacements? Absolutely—slip-in heaters are a top choice for replacing existing slip-in units in retrofits. Supply your current duct dimensions, cutout size, voltage, kW rating, airflow specs, insulation details, and any special needs for a precise, compatible replacement.

What maintenance is required? Perform regular inspections: check for airflow restrictions or blockages, tighten electrical connections, inspect heating elements for damage or dust buildup (clean in dusty environments), and test safety limits. Never run without airflow. Follow the unit-specific manual for detailed schedules, cleaning methods, and procedures.

How do I get a quote on a custom configuration? NorthStock specializes in custom slip-in electric duct heaters with fast shipping and expert support. Request a quote here — provide duct size, voltage, kW needs, airflow details, insulation thickness, and any custom features for a quick, accurate response.

Fast Shipping + Expert Support NorthStock supplies slip-in electric duct heaters for commercial and industrial applications, with fast shipping and knowledgeable support. We help customers: