When studying the anatomy of an HVAC sheet metal duct system, a natural instinct is to draw a comparison with the human anatomy. Arms, trunks and legs in a skeletal system come to mind, as do lungs and trachea in a respiratory system, as well as the heart in the circulatory system. A human body, with brains and nerves, is much more complicated, of course, but the comparison is still very useful when examining how ducts work.

Take take-offs, for example. When supplying air, a sheet metal duct system will typically divide the flow into outlets such as diffusers, grilles and registers. Round, oval or rectangular fittings called take-offs are carefully designed to take the correct amount of air flow from the main duct into each branch duct. Translate this into the human anatomy equivalent, and you can see the diaphragm contracting and causing air to flow into the airways — critical to the breathing process.

Absolutely central to ductwork anatomy is the plenum — the central distribution and collection air flow unit for an HVAC system. The supply plenum directs air from the central unit to the rooms which the system is designed to heat or cool. The return plenum carries the air from several large return grilles to a central air handler. The heart of the system, one might say.

Other key parts of the system include:

  • Volume Control Dampers which enable the volume of air flow to be adjusted.
  • Smoke & Fire Dampers seal off a duct when they detect smoke and fire.
  • Turning Vanes minimize air turbulence and help air flow at sharp changes of direction.
  • Stacks (vertical ducts) that allow air to travel vertically within relatively thin walls.

The ability to create first-class ductwork relies on sound knowledge and experience of its component parts, the equivalent of a highly-skilled surgeon, so to speak. Here at Roto-Die, we are not new to ductwork anatomy either, and are free at all times to discuss good design.