Many owners of older homes without forced-air HVAC systems, would like to add central air conditioning and/or heating ducts, but are daunted by the cost and difficulty of the installation process. Installation of ductwork may require removing large sections of walls, floors or ceilings, or adding unsightly box chases. However, high-velocity heating and cooling systems minimize these alterations by using small diameter ducts that can be more easily threaded through floor, ceiling, and wall cavities.Mini-Duct Air Distribution System Diagram
According to the manufacturers, these high-velocity systems operate quietly and improve dehumidification, room air mixing, and energy efficiency over standard air-delivery duct systems.
High-velocity heating and cooling systems use a special fan coil and air handling unit that generates high-pressure air forced through small diameter ducts. The main supply trunk is either a rectangular or round duct that supplies air to flexible, insulated, 2″ diameter plastic feeder ducts. Air passes through sound-suppressing tubing at the end of a duct run before entering the room through a plastic collar fitting. According to manufacturers, air is supplied at 440 to 1200 cubic feet per minute (CFM).
High-velocity systems use standard outdoor condensing units for air conditioning and heat pump systems. As an option, a water coil can be mounted in the air handling unit for boiler heating or chilled water cooling. Alternatively, adding a bank of electric heating elements to the air handler can provide heating capability to a high-velocity air-conditioning system. High-velocity system air handlers can satisfy cooling capacities between 18,000 and 60,000 BTUH and heating capacities between 24,000 and 143,000 BTUH.
The mini-duct air distribution system removes approximately 30% more moisture in the cooling mode than conventional systems. This results in cooler, dryer air. Lower humidity levels create a more comfortable environment, even at a higher temperature. The mini-duct air distribution system can be installed in any home, regardless of the design, construction, or age with little or no remodeling.
Ease of Implementation
The mini-duct air distribution system is quick and easy to install. The small flexible, insulated tubing is designed to fit the existing structure without major remodeling. The tubing requires approximately 1/10th of the space of conventional central air conditioning.
High-velocity air distribution systems are distributed by certified contractors or may be purchased directly from the manufacturer or distributor. However, it is important to note that some heating and cooling professionals are unfamiliar with high-velocity ducts. The systems commonly require a greater number of outlets–(about 5 outlets per ton of cooling, or one outlet for every 2400 BTUs of heating), –adding to material costs and installation time.
The initial costs for mini-duct systems are greater than their conventional counterparts.
U.S. Code Acceptance
The Air Conditioning and Refrigeration Institute (ARI) certifies high-velocity air distribution systems for use with numerous heat pumps, air conditioners, and heat sources.
High-velocity heating and cooling systems should be installed by manufacturer-authorized heating and cooling professionals. Small diameter ducts may be run through penetrations in floor joists, unlike systems with standard-sized ducts. Placing air outlets in areas of a room, such as in corners of a ceiling, or beside windows or doors, can result in a high-velocity output that improves room air mixture without causing discomfort to occupants.
The mini-duct systems typically carry a manufacturer’s warranty for a period of 1 year from the date of installation. However, some parts of the system may not be covered by this warranty. See store for details.
Manufacturers claim that dehumidification with high-velocity air distribution is better than for conventional forced-air systems. In the air conditioning season, lower humidity levels can allow occupants to feel comfortable with the thermostat set at a higher temperature, resulting in reduced energy costs. In both heating and cooling seasons, delivering air at higher velocity through smaller supply lines mixes the room air more effectively, reducing temperature stratification, and eliminating the need to place duct outlets at windows or exterior walls to avoid hot/cold spots.
For installation in existing homes, the 2″ supply lines can be fed through joists, wall cavities, and around common obstructions, so that costly and disruptive structural alterations can be avoided. This can be beneficial in applications where existing architectural features, like plaster moldings, would be difficult to change or duplicate. For this reason, high-velocity systems can be the most cost-effective option for retrofits, although they may be more expensive than conventional ductwork in new construction.