Mueller Streamline 4KMR6 Flex Duct 4in R-6 Foil 25ft

Product Description

The MUELLER STREAMLINE 4KMR6 is a flexible insulated HVAC duct designed for small-diameter branch runs where thermal performance and routing flexibility are both priorities. Built with R-6 insulation and a foil jacket exterior, it reduces heat gain and loss along the duct run more effectively than standard R-4 or uninsulated flex duct. At 4 inches in diameter and 25 feet in length, this duct is sized for individual branch connections from a plenum or trunk line to a supply register. HVAC technicians and sheet metal installers use this product in residential and light commercial forced-air systems where code-required insulation levels or energy efficiency targets call for higher R-value flexible duct.

This duct is commonly installed in attic spaces, crawlspaces, and unconditioned chases where ambient temperatures can cause significant thermal loss through duct walls. The 4-inch diameter suits single-room or zone branch applications. The 25-foot length covers most standard branch runs without a mid-run connection, reducing potential air leakage points. The foil jacket resists moisture and is compatible with standard flex duct fittings and sheet metal collars used in residential forced-air installations.

Key Features

• R-6 insulation provides higher thermal resistance compared to standard R-4 flex duct, reducing energy losses in unconditioned spaces
• Foil jacket exterior resists moisture and supports standard mechanical fastening and mastic sealing
• 4-inch inner core diameter suits branch duct runs to individual supply registers
• 25-foot length minimizes mid-run connections and associated leakage points
• Flexible construction allows routing around framing, joists, and obstructions without rigid fittings

Compatibility

Designed as an OEM-style replacement and standard installation flex duct for residential and light commercial forced-air HVAC systems using 4-inch branch connections and standard sheet metal collars or flex duct fittings.

Installation Notes

Installation should be performed by a licensed HVAC technician or qualified sheet metal installer in accordance with ACCA Manual D and applicable local mechanical codes. Power down the air handler and lock out the system before connecting or repositioning any duct sections. Secure both ends of the flex duct with approved draw bands or clamps and seal with UL 181B-listed mastic or approved tape — do not use standard cloth duct tape. Avoid sharp bends and excessive compression of the inner core, as both conditions restrict airflow and reduce effective R-value.