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Simply stated, the NEC defines a plenum area as, “a compartment or chamber to which one or more air ducts are connected and that forms part of the air distribution system.” It also references, “the space over a hung ceiling used for environmental air-handling purposes,” and, “areas beneath raised floors for information ...
In building construction Plenum is a separate space provided for air circulation for heating, ventilation, and air-conditioning. It is commonly found in the space between the structural ceiling and a drop-down ceiling or under a raised floor.
For the purposes of this code, a closet used as an air plenum that contains the blower unit or air handler of a central air-conditioning or heating unit.
A plenum in heating, ventilation, and air conditioning (HVAC) systems is a box or volume in the building structure that connects to the HVAC system. It has a critical function and that is to bring in, distribute, or remove air. Each HVAC system typically uses two plenum boxes: a supply plenum and a return plenum.
A mechanical equipment room is occupiable and therefore is not technically a plenum, but the code makes an exception for such. A mechanical equipment room is unique in that it is an enclosure that can be used as a ductwork plenum and can be occupied for maintenance.
It is typically provided in the space between the structural ceiling and a drop-down ceiling. A plenum might also be under a raised floor. In buildings with computer installations, the plenum space is often used to house connecting communication cables.
OK as a rule of thumb the closets need to be a total of 12 inches wider than the furnace. That means if furnace is 21" wide we need at least 12" combined space on each side (33inches wide). That can be 6" on each side, five on one side and 7 on the other etc as long as a total of 12".
A mechanical room, boiler room or plant room is a technical room or space in a building dedicated to the mechanical equipment and its associated electrical equipment, as opposed to rooms intended for human occupancy or storage.
A closet system with little airflow can cause mold to start growing. This is not only a surface-level problem; left unchecked, mold can cause structural damage to a home, as well as health issues in those spending time in the room, according to the Centers for Disease Control and Prevention.
Plenum cables are engineered with fire-retardant materials, emitting minimal smoke and toxic fumes in case of fire. Non-plenum cables may not possess the same level of fire resistance. Non-plenum cables often come at a lower cost than plenum cables, making them a more budget-friendly option for specific installations.
There is one component of this ductwork that has a big job, but its name isn't very well known–the plenum! There are actually two types of plenums, which are typically in a rectangular shape. The supply plenum is on one side while the return plenum is typically catty-cornered to it.
Expert-Verified Answer
A plenum is another term for the upper intake manifold, which plays a vital role in distributing the air-fuel mixture to the engine's cylinders. Its design impacts combustion efficiency and engine performance.
Plenums are limited to uninhabited crawl spaces, areas above a ceiling or below the floor, attic spaces, and mechanical equipment rooms.
Short Answer: When in doubt, use plenum-rated cable. This rating is specifically used in spaces that are typically above dropped ceilings, below raised floors, or in other semi-enclosed spaces used for air circulation.
Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum; however, some drop-ceiling designs create a tight seal that does not allow for airflow and therefore may not be considered a plenum air-handling space.
The mechanical rooms are the beating heart of a commercial building. It's where most, if not all, of the building's mechanical equipment is centered. Air handlers; boilers; chillers; heat exchangers; water heaters, tanks and pumps; back-up generators; even elevator machinery can all be found in these rooms.
Spaces such as boiler rooms, mechanical rooms, or electrical rooms are designed for a particular purpose and should not be seen as an opportunity for free storage within a building. Storing combustible materials within one of those spaces increases the risk and also the fuel load within the space should a fire occur.
Many of the house plans I review have some area inside the home or garage where these mechanical systems are planned to be located. Depending on the systems planned to be installed, it's often beneficial for the mechanical room to be located on an exterior wall.
An HVAC closet should be spacious enough to house the unit while allowing for adequate airflow and maintenance access. In general, the minimum dimensions for an HVAC closet are typically around 30 inches wide by 30 inches deep and 80 inches high.
In buildings sprinklered in accordance with NFPA 13, closets shall meet the following requirements: Closets of less than 12 ft2 (1.1 m2) in individual dwelling units shall not be required to be sprinklered.
It is a common misconception that a bedroom must have a closet. However, the legal requirements for a bedroom primarily concern health and safety rather than storage space. While some local markets may require a closet to consider a room a bedroom, most states do not mandate built-in closets.
Thus, fire and building safety codes mandate plenum-rated cables be used in plenum spaces and air ducts. They can also be used in non-plenum areas. Non-Plenum cables, on the other hand, are much cheaper and not as fire-resistant. When burned, they release toxic fumes such as hydrochloric acid and dioxin.
A plenum is a box or chamber that connects the air handling unit (AHU) to the ductwork in an HVAC system. It distributes conditioned air throughout the building and provides a return path for unconditioned air back to the AHU.
Traditional Post and Panel Raised Floor
A traditional access floor creates a sealed air space (called a plenum) between the raised access floor and the subfloor. The plenum is there to accommodate and contain underfloor air distribution (UFAD).