What are the different types of ductwork in HVAC

The main types of ductwork in HVAC systems include: (1) Flexible ducts (flex duct)—corrugated, flexible tubes typically made of wire coil covered with plastic and insulation, easy to install in tight spaces, commonly used for final connections to room vents; (2) Rigid sheet metal ducts—made from galvanized steel or aluminum, rectangular or round shapes, most durable and efficient but more expensive and difficult to install; (3) Fiberglass duct board—rigid panels of compressed fiberglass with foil facing, formed into rectangular ducts, provides built-in insulation and sound dampening; (4) Fiberboard ducts—made from compressed resin-bonded fiberglass, similar to duct board, good insulation and acoustics but less durable than metal.

Beyond material types, ducts are categorized by shape: round/circular ducts (most efficient for airflow, less friction loss, common in commercial applications), rectangular ducts (fit better in tight spaces like between ceiling joists or wall cavities, common in residential applications), and oval/flat oval ducts (compromise between round and rectangular, used where height is limited but width is available). Ducts also classify by function: supply ducts (carry conditioned air from HVAC unit to rooms), return ducts (carry air back from rooms to the unit), and exhaust ducts (remove contaminated air outside). Sizing categories include trunk lines (large main ducts carrying most airflow), branch lines (smaller ducts splitting from trunks to individual rooms), and boots/transitions (connect ducts to registers and grilles). Each type has advantages and appropriate applications: flexible duct is cost-effective and easy to install but can restrict airflow if over-bent or compressed; sheet metal is most durable and efficient but expensive and labor-intensive; fiberglass provides insulation but can degrade and potentially release particles. Professional HVAC design selects ductwork types based on building layout, budget, efficiency requirements, local codes, and specific application needs. Properly designed, installed, and sealed ductwork is essential for HVAC system efficiency—leaky or poorly designed ducts can waste 20-40% of heating and cooling energy.