July 29, 2026 · 6 min read
Where rigid metal earns its cost
Main trunks, long runs and anything in a mechanical space should be rigid. It holds shape, cleans well and lasts decades.
Rigid also gives you predictable friction losses, which matters when the design is tight.
Where flex is the right call
Short final connections to registers, especially where a gentle offset is needed, are a good use of insulated flexible duct.
Kept short, pulled tight and properly supported, flex performs well.
How flex goes wrong
Sagging between joists, compression at bends and excess length coiled in an attic destroy airflow. These are installation failures, not material failures.
Flex is also difficult to clean aggressively, which matters over a 20-year horizon.
- Supported every four feet minimum
- Stretched fully, no slack
- No bends tighter than the duct diameter
- Inner liner clamped separately from insulation
- Runs kept under about eight feet
Our default approach
Rigid trunk and branches, insulated flex only for short final connections, and every joint sealed with mastic.
It costs more than an all-flex install and outperforms it for the life of the house.
Related service
Air Duct Installation
Custom ductwork installed for efficient airflow in new builds and renovations.
See Air Duct Installation details