Air Duct Efficiency

Air ducts lose or gain heat whenever your hvac equipment is running. If the temperature inside your duct is different from the air outside, then a heat loss or gain will occur. This loss or gain is something that needs to be considered when designing ductwork in a home or office. This aspect of heat transmission will depend on some or all of the following factors:

•  Temperature of the air in the duct
• Air velocity in the duct
• Ambient temperature
• Air duct insulation

If the ducts are used to convey heat, excessive heat loss from the air ducts will reduce the efficiency of the heating system. This will result in a total loss of heating effect if the heat loss occurs in the ductwork passing through an unheated area but it can be considerably reduced with proper insulation.  This heat loss can also occur in heated spaces but run the risk of poor air distribution.  These same conditions exist when the ducts carry cool air.  When air passes through spaces subject to the cooling effect of air conditioning insulating the ducts will effectively reduce the amount of heat gain.

Air velocity will also influence the amount of heat gain in the ductwork. High air velocities are recommended when the ducts are carrying cool air because their effect is to reduce the amount of heat gain pickup in the ducts; however they need to be maintained consistent with the acoustic requirements of the installation.

Air Duct Leaks
Air leakage through ducts seams and holes will result in the loss of a portion of the air flowing through the duct and a proportionate reduction in the heating or cooling effectiveness of the system. Depending on the seriousness of the problem, the ductwork can lose up to 1/3 of the air supply in this manner. It is usually a matter of poor workmanship and can be corrected by sealing the seam cracks and holes by calking or soldering.  You can also contact an energy contractor in your area to help you seal your air ducts.

Air Duct Insulation
Air ducts are insulated to prevent the excessive heat loss or gain we've been talking about.  It is a great solution for homes or offices that have older ductwork or a furnace that is not very efficient.  To maintain the proper level of performance in a heating or cooling system, the following ducts should be insulated:

• Long supply ducts (any over 40 ft in length)
• Supply ducts running through spaces that are neither heated nor cooled such as ducts located in the attic, basement or garage
• All ducts located on the outside of buildings
• Cool-air return ducts passing through hot areas such as boiler rooms, kitchens or furnace room

When you have round air ducts, use insulation with flexible fiberglass insulation.  If you have square ducts you can use flexible and slab insulation.  These lightweight semirigid panels are available with a variety of facings for appearance and functional use.

Flexible and slab insulation can also be made as duct liners for absorbing duct system noise.  One or both sides are coated to reduce air friction loss and bind surface fibers and insulate thermally.  Flexible insulation is secured in place with light-gauge wire ties. Slab insulation is secured to the duct surface with adhesive or mechanical clips.  It is recommended that a vapor barrier be placed between the insulating material and the duct surface to prevent the formation of condensation. The vapor barrier should be used when the temperature of the air inside the ducts is lower than the dew-point temp of the surrounding air in the duct.

If you are unsure that your ductwork is properly sealed and as efficient as it can be, contact a local hvac company for an inspection.  If you are in Colorado, I recommend checking out Million Air Mechanical at (303) 568-3709 or visit their office 4892 Van Gordon St #202 Wheat Ridge, CO 80033 or visit their website Furnace repairs Denver.