The performance of the air distribution or duct system of a home is critical to the efficiency of the air conditioner and furnace, to the comfort of the occupants and to the ability of the system to maintain a low humidity level to stop mold from growing.

The impact of leaky ducts on a building’s total utility consumption can be large.

Most people are surprised to see that duct leakage exceeds the combined impacts of wall and ceiling leakage.

Leaky ducts graph

Studies conducted by several Texas utilities, the U.S. Department of Energy and major universities around the country conclude that the average duct system in a Texas home loses 25% of all the cooled or heated air that passes through the unit. This terrible waste costs the average Texas consumer about $100 per year, and results in high indoor humidity levels, less comfortable homes and poor indoor air quality.

The new state energy code, the International Energy Conservation Code (IECC), allows the use of both standard approved tapes and mastics as duct sealing materials. However, there is a very significant difference in longevity and performance between the two products. The U.S. Department of Energy tested both tapes and mastics. They found that even the new tapes failed after ten years, while the mastic sealed ducts did not fail after sixty years of accelerated aging tests. Maintenance of ducts is often impossible due to their placement between floors and in walls. Therefore, they should be sealed with materials that will last for the life of the building. This means using approved duct mastics.

Duct leakage directly causes the addition of 25-50% increase in the size of an average air conditioner to compensate for the loss. The builder pays the added cost of larger equipment during construction. The family pays in greatly increased utility costs and in poor air quality for the life of the home, and society pays in increased air pollution for decades.