Air distribution system ducts are designed to supply conditioned air from space heating and cooling equipment to the living spaces and return an equal volume of air from the living spaces back to the heating and cooling equipment to be conditioned. Ducts are usually located in unconditioned spaces such as attics, crawlspaces, garages, or unfinished basements and made out of thin materials that easily conduct heat.

Due to the extreme winter and summer temperatures in these spaces, 10 percent to 30 percent of the energy used to heat and cool the air is lost to conduction through the duct surfaces. In order to maintain temperatures at a comfortable level, the heating and air conditioning equipment has to compensate for this heat loss or gain by conditioning additional air. Thus, uninsulated or poorly insulated ducts reduce the efficiency of the heating and cooling systems and increase energy bills.

Comfort

Uninsulated or poorly insulated ducts can also cause occupant discomfort, especially during the winter months. As conditioned air moves through As a result, rooms served by long duct runs can experience “cold blow” because they typically have lower heating supply air temperatures. This problem can be more pronounced with heat pumps that deliver air at lower temperatures.

Even when the furnace or air conditioner is not operating, heat loss occurs due to conduction through the duct surfaces. The need for insulation can be reduced if the ducts are located within the conditioned space. In this location, any conductive losses and gains would be minimal since ducts would be exposed to indoor air temperatures. Some insulation is still required to ensure that the conditioned air is delivered at the desired temperature, and to prevent condensation on duct walls. The ENERGY STAR Program promotes the proper insulation of ducts as a means of improving system efficiency and lowering utility bills.

Benefits

Duct insulation can provide many benefits including: Improved comfort. Duct insulation minimizes conductive heat losses and gains, allowing supply air to be delivered closer to design temperatures. In winter, “cold blows” will be reduced in rooms supplied with long duct runs. This can result in quicker recovery from night-time setbacks and a more consistent level of comfort throughout a house.

Lower utility bills

The average homeowner spends over $1000 per year on just heating and cooling. Duct insulation minimizes conductive heat losses and gains and reduces heating and cooling systems’ operating time. This results in lower utility bills, making homes less expensive to operate. Lower equipment cost. Duct insulation can reduce space conditioning loads and, in some cases, allows for the installation of smaller, less costly heating and cooling equipment.

To improve energy efficiency for an existing home, thermal images from an energy house inspection or home energy audit will reveal many of the leaks in the ductwork behind walls. After the review you will have a roadmap to proper weatherization. Whether you are the do it yourself, "DYI" person or want to hand off to a contractor or handyman, the roadmap will help you make the best decision first. Fixing whats found will greatly improve your comfort, savings and reduce your carbon footprint.

Before insulating ducting, see our article on Duct Sealing to reduce system loss.

Content Courtesy US EPA