Air-Distribution Systems: Overhead and Under-Floor

Without a reliable way to move heated or cooled air from your furnace, air conditioner or heat pump, even the most efficient equipment will be unable to keep the indoor spaces of your residential or commercial building comfortable. During the design phase of your project, carefully plan for the best and most efficient air-distribution systems possible. The extra care you expend at this point will pay off in increased energy efficiency and ongoing monthly savings over the life of the building.

Air-Distribution Systems: The Basics

Air-distribution systems serve as the pathway for conditioned air to travel from your HVAC equipment to the spaces inside your building. They usually consist of a long network of metal ducts arranged in a pattern that allows for efficient dispersal of air. When heated or cooled air is produced by your HVAC system, the air is blown into the ductwork using powerful fans or air handlers. The air exits from vents and either increases or decreases the temperature in the building. Return ducts bring air back to the HVAC unit to be filtered, reconditioned and redistributed.

The design of air-distribution systems will be influenced by the physical configuration of your building and the available space for installing ductwork. Care must also be taken to ensure the ductwork remains in good condition with all connections tightly sealed to prevent air leaks and energy loss.

Overhead Air-Distribution Systems

Overhead air-distribution systems are usually installed in ceiling spaces. The ductwork is placed behind drop ceilings or similar structures. Overhead air-distribution systems disperse air into indoor spaces through vents and diffusers in the ceiling or placed high up on the room’s wall. Supply air coming from these systems is generally between 50 and 55 degrees. The conditioned air mixes with the room air to produce heating or cooling that will keep occupants comfortable at the level where they work or live. There is usually little difference in the temperature of the air at floor level or ceiling level.

Under-Floor Air-Distribution Systems

Under-floor air distribution systems are installed beneath the floor of the building. Air travels through the ductwork and exits from vents and diffusers that are also installed in the floor. Sometimes these systems use a plenum under a raised floor; the conditioned air accumulates in the plenum and is then distributed to the spaces above. Air coming out of under-floor systems is usually between 60 and 65 degrees. Heated air then rises toward the ceiling, warming the occupants of the room and keeping the temperature of the space at occupant’s preferences. There can be significant differences between temperatures at ceiling and floor levels when using this type of air-distribution network.

In general, under-floor air-distribution systems are more efficient and cost-effective than overhead systems. They are easy to incorporate as a structure is being built, which helps keep the cost of installation low. They also offer benefits such as:

• Reduced energy use resulting in ongoing cost savings on seasonal heating and cooling expenses: Under-floor ducts lose less energy than their overhead counterparts, which helps keep costs down. The higher temperatures of supply air also mean HVAC equipment has to run less.
• Better flexibility in the use of the indoor space: Without overhead ducts or vents, the indoor space can be designed for better practical function or decorative use.
• Improved indoor air quality: Under-floor systems typically support better indoor air quality than overhead air distribution networks. Clean ventilation air can be supplied directly to the room without the need to mix it with existing room air, which reduces the amount of airborne particulates.
• Dual-purpose function: Under-floor systems can often be used for a secondary purpose, such as a pathway for directing and securing electrical wiring.

Our goal is to help educate our customers about Plumbing, HVACR, Fire Protection and Alarm Systems in Mechanical, Commercial and Residential settings. For more information on designing and installing effective air-distribution systems, or to view projects we’ve worked on, visit our website!