What is the difference between a plenum and a duct?

airflow. A plenum is an air distribution box designed for forced-air systems on residential homes and commercial businesses. It is part of the ductwork, but far different than an air duct as these important boxes handle air as it enters the ducts and helps to recirculate it within a system.

What is the purpose of a plenum?

Plenum boxes are usually situated on either side of the fan or heat exchanger and have the important function of bringing in, distributing, and removing air. They are the air's first stop after being heated or cooled and its last stop before going back into your AC, heat pump, or furnace.

What is the plenum in duct?

The supply plenum is an air distribution box. It's attached directly to the supply outlet of the HVAC equipment–that is, the outlet that releases chilled or heated air into your home. The air ducts that distribute the air into the individual rooms of your living space all connect to this plenum.

Do I need a plenum?

Most residential buildings don't have plenum airspaces. Plenum areas are more common in commercial buildings. However, if your house does happen to have a plenum airspace or you need to run cables through an air duct, then plenum-rated cable is required.

Why is it called a plenum?

The term "plenum" was coined in the 1670s, derived from Latin adjective plenus ("filled, full"). The usage originates from classical theories of physics and the notion that "nature abhors a vacuum".

Titus Timeout Podcast - What is Plenum Return?

Is an open ceiling considered a plenum?

Plenum spaces are the open spaces above the ceiling or below the floor that are used for air circulation. Technically, any ductwork is considered a plenum space too.

Is a drop ceiling a plenum?

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.

Where is plenum required?

If you have a large wall or ceiling return air grate; remove and see if there the air is channeled through sheet metal ducting. If there is no sheet metal duct; just the open ceiling or wall space, then you are required by law to use Plenum Rated cable.

What size should my plenum be?

Single plenums should not exceed 24 ft in length. Double plenums should not exceed 48 ft in total length.

What's the difference between plenum and non plenum?

Plenum Cable Explanation

This cable is made from less hazardous and lower smoke materials than non-plenum cables, which is approved by UL (Underwriters' Laboratories) for non-conduit applications located in environmental air spaces. The cable is designed to restrict flame propagation and limit the amount of smoke.

What is the duct?

any tube, canal, pipe, or conduit by which a fluid, air, or other substance is conducted or conveyed. Anatomy, Zoology. a tube, canal, or vessel conveying a body fluid, especially a glandular secretion or excretion.

What is a plenum in plumbing?

In building construction, a plenum (pronounced PLEH-nuhm, from Latin meaning full) is a separate space provided for air circulation for heating, ventilation, and air-conditioning (sometimes referred to as HVAC) and typically provided in the space between the structural ceiling and a drop-down ceiling.

What is a plenum and where can I find one?

What Is a Plenum Box? A plenum box is an HVAC component consisting of an enclosed box that's connected to the ducts. You can usually find them around your HVAC system's air handler or furnace, which of course is also where the filter is located.

What are the 4 types of duct systems?

Namely, flexible ductwork, rigid ductwork, and semi-rigid ductwork. We've compiled information on each of these duct systems. These ducts are typically tube-shaped and made of a wire coil covered with a bendable, durable plastic, and surrounded by insulation.

What size plenum do I need for a 5 ton unit?

For 5-ton HVAC systems, an additional 6" plenum on the bottom or the side of the furnace is super important.

What size duct do I need for a 12x12 room?

A 12×12 foot room will need a 4×8 inch supply duct to get an adequate CFM rate, which is about 144 CFM.

Is PVC plenum rated?

Fact: PVC should not be installed in a plenum. It is classified as a combustible material per ASTM E 136.

Is Romex plenum rated?

Regular type NM cable (what's generally called Romex) is not plenum rated. Type AC cable (often incorrectly called BX) is allowed in plenums, however. The main concern is the toxic fumes that the plastics used in most wire insulation release when they're heated or burned.

How do you identify a plenum ceiling?

A plenum ceiling is one that uses the space between the top of the suspended ceiling and the bottom of the floor above to handle air for ventilation. All suspended ceilings are not plenums; some may use HVAC ductwork to move air to returns and diffusers located in the ceiling tiles (a 'dead' ceiling).

What is the space above ceiling called?

If there is a horizontal ceiling that is attached to the tie-beams of a roof, creating a space above it, the space above is called an “attic” whether used as a living, storage, or simply ventilation space.

What is the space above a drop ceiling called?

The area above the dropped ceiling is called the plenum space, as it is usually used for the HVAC air return. The plenum space is also very commonly used to conceal piping, wiring, and ductwork.

Is drywall plenum rated?

By exception 5, the only way to cover non-plenum rated materials in a plenum is with either a drywall assembly or with materials specifically listed and labeled for covering items in a plenum. The only listed material I know of is a plenum wrap similar to the fire wrap used on grease duct.