4 Inch 90 Degree Duct Elbows — Dimensions & Specifications

The takeoff dimension for a 4-inch long-radius 90-degree elbow refers to the straight-line distance from the elbow's end to the point where the curve begins. For a 4-inch long-radius elbow (1.5D centerline radius = 6 inches), the takeoff is typically equal to the centerline radius — approximately 6 inches on each leg.

The circumference of a 4-inch round duct is calculated using C = π × D, where D is the diameter. For a 4-inch duct: C = 3.1416 × 4 = approximately 12.57 inches. This measurement is important when fabricating fittings, determining material requirements, or connecting duct sections with collars and bands.

4-inch 90-degree duct elbows are typically available in galvanized steel, stainless steel, and aluminum, depending on the application. Galvanized steel is standard for general ventilation, stainless steel suits corrosive environments, and aluminum is preferred where lightweight construction is required. Contact Duct Incorporated to confirm available material options.

A short-radius elbow has a centerline radius equal to the duct diameter (1D), resulting in a tighter bend with higher airflow resistance. A long-radius elbow uses a 1.5D centerline radius, providing a smoother airflow path and lower pressure drop — making it preferred in industrial ventilation and dust collection systems where efficiency matters.

Yes, 4-inch 90-degree duct elbows from Duct Incorporated are suitable for dust collection systems. They are designed to handle particulate-laden airflows and provide reliable direction changes within collection ductwork. For abrasive materials, ensure the elbow material and gauge are rated for your specific dust type and system velocity.

4-inch duct elbows are connected using slip-fit or crimped-end joints, secured with sheet metal screws and sealed with duct tape or mastic sealant. Ensure the elbow end matches your existing duct connection type — either plain or crimped. For dust collection or industrial exhaust, use band clamps or flanged connections for a more secure, airtight fit.