The Big Deal About Ducts

When it comes to home energy performance in the Greater St. Louis area, many people take for granted that simple home improvements such as adding insulation or upgrading to a new furnace or air conditioner can make a big difference. Those people are often correct and just as often...overlook the importance of ductwork.

As an example, think of a 95% efficient furnace using natural gas. The natural gas entering the home contains energy. The furnace is able to convert 95% of that energy into heat. Then the heat enters the ductwork.

How heat is lost throughout the ductwork

Heat is distributed all throughout the house by the ductwork. Along the way, some of the heat is lost due to imperfections in the ducts. Most of these heat losses comes from heated air leaking out through the seams in the ductwork - where the sheet metal is joined. Additional heat is lost if the ducts are not properly insulated. Heat losses are greatest if all the ducts are located “outside” the conditioned space, such as an attic or crawlspace.

Loss of heat (and cooling) through leaky, uninsulated ductwork can be the single most significant energy waster in a home. Using the example of the 95% efficient furnace from above, if 50% or more of the ductwork is located "outside" the home and if the ducts have a normal amount of air leakage, then the efficiency will likely fall to 70% or below for the furnace. If those same ducts are not insulated, the efficiency will fall even lower.

Distribution challenges with leaky and un-insulated ductwork

Leaky and uninsulated ducts can also cause distribution challenges. If our example, if the 95% efficient furnace is located in a basement and all the ductwork is located “inside the home”, then losses through leakage will also remain inside, but the loss means the heated (or cooled) air is not distributed properly throughout the home.

Poor distribution can cause uncomfortable situations. For example, the upstairs portion of the home may be hot in the summertime if some or even all of the air from the air conditioner in the basement does not arrive upstairs. Other portions of the home may be cold in winter if the heated air does not reach them.

Sealing leaky ducts and insulating them can be the single most cost-effective home improvement a St. Louis homeowner can make. This home improvement can also make a big difference in comfort and energy saving. In the end, sealing and insulating ducts really is a big deal.