A PLUS HVAC Inc.

Good Duct Design Increases Efficiency

Central heating and cooling systems use an airdistribution or duct system to circulate heated

and/or cooled air to all the conditioned rooms in a house. Properly designed duct systems

can maintain uniform temperatures throughout the house, efficiently and quietly.

WHY DUCT DESIGN IS IMPORTANT

The efficiency of air distribution systems has been found to be 60-75% or less in many

houses because of insufficient and/or poorly installed duct insulation and leaks in the duct

system. Properly designed and installed ductsystems can have efficiencies of 80% or more

for little or no additional cost, potentially saving a homeowner $50-200 or more per year

in heating and cooling costs. Moreover, efficient duct system designs can reduce

equipment size, further saving money for new or replacement equipment.

Duct systems that leak and/or do not distribute air properly throughout the house

may make some rooms too hot and others too cold. Leaky and unbalanced duct systems may

force conditioned air outside and unconditioned air into the house. This

increases heating and cooling costs and may also draw humidity, dust, mold spores, and

other contaminants into a home from the attic, crawlspace, or garage and radon gas from the

soil. In extreme cases, poorly designed and installed duct systems can induce

backdrafting—spillage of flue gases from combustion appliances (e.g., furnace, water

heater, fireplace) into the living space— primarily when atmospheric or natural-draft

flues are used rather than powered combustion systems.

Duct systems that are undersized, are pinched, or have numerous bends and turns may lead

to low air flow rates and high air velocities. Low air flow rates cause the heating and

cooling equipment to operate inefficiently. High air velocities increase noise.