What is VAV boxin construction?

A constant air volume (CAV) system delivers a fixed airflow and varies the supply air temperature to control the space, while a VAV system holds supply temperature roughly constant and varies the airflow through terminal boxes. VAV is the standard for multi-zone US commercial offices because each zone gets its own box and thermostat. For the estimator, the practical difference is the count: a VAV job carries dozens of terminal units, controls, and reheat connections that a CAV layout does not.

No. Interior zones that need cooling year-round are often served by cooling-only boxes, while perimeter zones that lose heat through the envelope typically get hot water or electric reheat. The equipment schedule identifies which boxes carry coils. The distinction matters at bid time because a reheat box adds a coil, a control valve, hydronic piping or an electrical circuit, and insulation, which can roughly double the installed cost of that line.

The sheet metal or mechanical contractor typically furnishes and hangs the boxes and makes the duct connections. The building automation or controls contractor mounts actuators and zone sensors, the hydronic piping crew pipes any hot water reheat coils, and the electrician powers fan-powered or electric reheat boxes. Because the scope splits across three or four subcontracts, scope sheets should name who provides, who installs, and who wires each component, or the gaps surface at buyout.