Plenums:
A plenum is a box that connects directly to the central HVAC system and serves as the main point for air distribution.
There are two types: Supply Plenum (distributes heated/cooled air to the ducts) and Return Plenum (collects used air and recycles it).
The Supply Plenum connects to the air handler or evaporator coil, distributing air throughout the structure.
The Return Plenum is typically larger to allow slower air movement, enhancing filtration efficiency.
Turning vanes may be required for even air distribution across filters or coils, especially in geothermal systems.
Transitions:
Used to connect ducts of different sizes and maintain airflow and air pressure throughout the system.
Transitions should be smooth, avoiding abrupt changes or angles to prevent turbulence and airflow restriction.
Common in retrofit situations, such as when new equipment is connected to existing ductwork.
Trunk Ducts:
The main horizontal duct connected to the plenum, also known as the trunk line.
Supplies air to various parts of the building, usually perpendicular to floor joists and supported with hangers.
Trunk ducts are typically rectangular and come in standard sizes (8 to 10 inches deep for residential systems).
A plenum takeoff or transition takeoff is used to connect the trunk to the plenum.
Branch Ducts:
Branch ducts are connected to the trunk line and supply air to individual rooms.
They can be round or flex duct, with round ducts typically supported every five feet.
Flex ducts are easier to install and seal, making them a preferred option in some systems.
Branch ducts are connected to the trunk using a fitting called a takeoff, and the connection is secured with screws, tape, or zip ties.
Fittings:
Takeoffs allow air to move from the trunk to the branch ducts.
Register boots transition from round branch ducts to rectangular shapes for registers and are installed in floors, walls, or ceilings.
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