All About Duct Insulation

Getting the most out of your air ducts

Although sometimes neglected in favor of an emphasis on heating and cooling units, thorough and effective duct installation ensures energy efficiency, safety, and cost effectiveness in any heating, ventilation, and air conditioning system.  Local regulations determine the quality and grade of insulation required.

Furthermore, ducts often run through unfinished or unheated areas (such as an attic, crawlspace, or basement), where extreme cold and heat conditions can affect the conditioned air inside the ducts.  Inadequately insulated ducts allow heated air to cool before it can be distributed through a vent (or let cool air warm), making the whole system less efficient and more costly to operate. Anywhere from 10 to 30 percent of the energy used to heat and cool the air can be lost to conduction through the duct surfaces. 

In order to maintain the desired temperature, heating and air conditioning equipment must compensate for this heat loss or gain by cycling additional air. Thus, uninsulated or poorly insulated ducts drastically reduce the efficiency of the heating and cooling system and increase energy bills.

Why Should I Care About Duct Insulation?

Benefits

Duct insulation can provide many benefits including:

Improved comfort. Duct insulation minimizes conductive heat losses and gains, allowing supply air to be delivered at the desired temperature. In winter, "cold blows"-a heater pumping out cold air-can be eliminated in systems with long duct runs.  A more efficient system can more quickly heat or cool a room after disruptions in temperature caused by overnight lows, an inactive system, or a sudden change in weather conditions.

Lower utility bills. Heating and cooling costs compromise a significant portion of a home's operating budget. Duct insulation minimizes conductive heat losses and gains and reduces heating and cooling systems' operating time. This results in lower utility bills.

Lower equipment cost. Duct insulation can reduce space conditioning loads and, in some cases, allow for the installation of smaller, less costly heating and cooling equipment.

How Do I Install It Right?

What to look for

Good duct insulation starts with a thorough sealing of all the joints in the duct run.  Well-sealed joints promote a quick, efficient flow of air through the system. Duct tape will not suffice for this purpose, since the tape degrades and decomposes over time, leaving the joints susceptible to leaks. 

Once the ducts have been sealed, an insulating jacket is wrapped around the ducts and plenum. Much like wall insulation, duct insulation is often made of fiberglass. The fiberglass surface faces in toward the duct, while the foil face protects the outside of the wrap, preventing conductive heat loss and protecting the fiberglass within. The insulation is applied in sheets that are cut to fit and seamed.

More information on ducting