What is a Ventilation Duct?

Sherry Holetzky

HVAC stands for heating, ventilation, and air conditioning. Ventilation is part of the process of heating or cooling air, which creates comfortable temperatures in a space. Air must be moved to and from a heating or cooling unit. Heated or cooled air, also known as conditioned air, is then moved out to the living or working space. This is done through the use of a ventilation duct. As the conditioned air is delivered, an equivalent amount of air must then be moved to the unit once again so it too can be conditioned.

An air vent grating covers the end of a ventilation duct.
An air vent grating covers the end of a ventilation duct.

While many homes today are built airtight for greater energy efficiency, the ventilation process helps substitute fresh air for stale air, which is then exhausted from the space. Both can occur by way of ventilation ducts. Some HVAC systems, often in commercial environments, allow the same air to be recycled or reconditioned. This is simply transferred air and not recommended. Too many pollutants can contaminate air and diminish oxygen, requiring another method of ventilation or air purification to obtain and maintain optimal air quality.

The construction and placement of a ventilation duct can impact the air conditioner's performance.
The construction and placement of a ventilation duct can impact the air conditioner's performance.

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Such systems may employ intermittent ventilation, which means certain high-risk areas are ventilated quickly to remove contaminants or even moisture. A good example is the use of an exhaust fan. However, in many residential settings, continuous or central ventilation is preferred. Continuous ventilation is simply the process in which stale air is replaced with fresh air on a slow yet steady basis.

The ventilation duct system is generally designed in a way that allows for the most efficient delivery of fresh air to the system and conditioned air to the receiving spaces. The less air has to travel, the less likely it is to lose temperature or to be contaminated. A ventilation duct, or parts of it, may be made from rigid or flexible material. Flexible parts of the ventilation duct are generally smaller lengths, frequently used to conveniently attach rigid ductwork to the system. Flexible materials may also be used in other difficult to manipulate spaces.

With central HVAC systems, the ventilation duct, its construction and placement, are important parts of the overall conditioning and delivery process. Intakes and outlets must be appropriately spaced and vented in order to keep fresh air from being contaminated by stale air. When air mixes, it not only hinders the performance of the system, but it also diminishes air quality. Ventilation duct leaks can also create air quality problems as well as inefficiency, so proper HVAC maintenance is essential.

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