The Challenge

A client needed to connect a portable air conditioning unit to an existing ventilation system, but encountered a common compatibility issue: a mismatch in ducting sizes. With no off-the-shelf 8-inch to 5-inch reducers available at local hardware stores, the AC unit was unusable without a custom-engineered bridge between the two diameters.

The Solution

Designed from scratch in Fusion 360, this adapter was modeled using a lofted geometry to ensure smooth airflow and minimal backpressure. The part was engineered with a precise friction-fit tolerance, allowing it to slide securely onto the AC unit’s exhaust and the ventilation duct without the need for mechanical fasteners or messy adhesives.

To handle the structural load of the heavy-duty flexible ducting, the wall thickness was increased beyond standard settings. PLA was used for the initial deployment to provide a rigid, dimensionally accurate fit that could withstand the immediate pressures of the cooling system.

Key Features

Material: Rigid PLA
Design Software: Fusion 360
Function: 8" to 5" diameter reduction
Fitment: High-precision friction fit for tool-less installation
Engineering: Lofted internal geometry for optimized airflow
Application: Home climate control / HVAC adaptation

The Result

The custom adapter allowed for the immediate installation and operation of the AC unit. By bypassing the search for rare injection-molded parts, the client was able to move from a cooling problem to a functional solution in less than 24 hours—demonstrating the speed and utility of on-demand engineering.

Custom 8" to 5" HVAC Duct Adapter