The proper way to install flexible ducting requires careful planning and execution:

1. plan the layout taking into account access, clearances and minimising bends.

2. load calculations, duct design and casing sizing are carried out prior to installation.

3. Use hard pipe for bends, elbows, and direct-from-duct installations; use hose for straight pipe.

4. tension flexible duct during installation to maintain smooth inside surface.

5. seal seams with mastic or metal tape to prevent air leakage.

6. properly anchor ductwork to prevent sagging or kinking.

7. keep proper distance from heat sources to avoid damage.

8. Make sure there are no obstructions in the ductwork.

9. test and balance the system after installation, check static pressure and airflow, and make adjustments if necessary.

Observing local building codes and manufacturer requirements is crucial, and if you are not confident in the installation process, it is recommended that you hire a professional HVAC technician.