What is a Terminal Unit?

Mary McMahon
Mary McMahon

A terminal unit is an outlet in ductwork to allow air delivery to an environment like a room. The terminal unit taps into the ducts with a fan to push air out of the ductwork at varying speeds to control the environment. Terminal units may also have built in heating and cooling coils, depending on the installation. A technician installs these components of a heating and cooling system during the initial process of setting up the system. If adjustments need to be made in the future, the technician can return to move or cut off terminal units.

A terminal unit can be fabricated from sheet metal.
A terminal unit can be fabricated from sheet metal.

When a technician prepares to install a terminal unit, the planning of the ductwork is taken into account. The unit needs to be the right size for the application. The technician considers the size of the ductwork, the room connected to the terminal unit, and other factors to install a unit of the right size. It is possible to fabricate units with fans and sheet metal, or to order a terminal unit of generic size and shape from a manufacturer. Manufacturers of ductwork often produce matching terminal units for convenience.

Usually, the ductwork divides a structure into thermal zones, with one terminal unit in each zone to control temperature. In cases where a thermal zone is unusually large, more units may be installed to keep the temperature stable. The air terminal unit's placing has to be carefully considered for maximum efficiency, and because the area around the outlet needs to remain clear, the technician also needs to consider the least inconvenient option for positioning.

In remodeling and retrofitting, it may be necessary to relocate terminal units. Unused sections of ductwork can be closed off so air does not flow through them, and a technician can create new connections and branches to accommodate the needs of the remodel. In cases where a building is substantially increased, the technician may need to retrofit the entire ducting system to address the change in size; narrow ducts designed for circulating sufficient air for a small space will not be up to the task of a radically larger one, or the airflow may not be efficient after the remodel.

A terminal unit commonly has a grating over the fan to keep material out of the ducts and reduce the risk of injuries caused by bumping up against the fan. Periodically, a technician or cleaner should remove the grating for cleaning. While it is exposed, the fan and duct can be cleaned as well. Reducing dust in the ductwork increases safety and will keep the air fresh and clean. In rare cases, bacteria can colonize ducts if they are kept warm and moist, and a deeper cleaning may be necessary.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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