Description

20″ x 4″ Transition Box 

20″ x 4″ Transition Box is the perfect fit. Designed for use in marine vessels, RVs, and other confined environments, this low-profile box is engineered to deliver efficient, quiet airflow in areas where space is extremely limited—but comfort is non-negotiable.

With its sleek 20″ x 4″ size, this transition box is ideal for narrow bulkheads, overhead cabinetry, slim wall cavities, or under-furniture installations. The elongated shape allows for a wide, even spread of airflow, making it especially effective for cooling long or narrow areas while maintaining a low visual profile.

This box is fully compatible with MSI grilles and ducting systems, ensuring seamless integration with both flexible ductwork and your choice of air outlets. Whether you’re using wood-framed or plastic-framed grilles, the 20″ x 4″ Transition Box creates a tight, secure fit that promotes efficient air delivery while minimizing leaks and energy loss.

Whatever your choice, wood-framed or plastic-framed grilles, you will require a way to effectively duct the chilled air to them. We offer a wide selection of plastic ducting products—from the hose adapter on the air handler to the transitions behind the grilles. The 20″ x 4″ Transition Box is an essential component in that lineup, designed for installations where a low-profile form is key.

Built from high-quality, lightweight, and corrosion-resistant materials, this transition box is made to handle the vibration, temperature changes, and moisture exposure common in mobile and marine HVAC environments. Despite its slim size, it maintains excellent airflow integrity and noise control, helping to ensure occupant comfort in every space.

This item ships direct from the manufacturer, ensuring factory-level quality assurance and timely delivery for your installation needs.

Key Features:

• Ultra-slim 20″ x 4″ design – ideal for tight or narrow spaces

• Compatible with MSI grilles and ducting systems

• Supports both wood and plastic-framed grille styles

• Promotes even airflow and efficient system performance

• Durable, lightweight, and corrosion-resistant construction

• Ships direct from the manufacturer

Choose the 20″ x 4″ Transition Box for precision air delivery in long, narrow, or low-clearance HVAC installations.