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  • Writer's pictureKeith Groninger

AC Ducts in the Attic

Updated: Dec 11, 2023

The Greenhouse Effect causes a typical attic to become super-heated in the summertime. This is the same effect that causes the inside of your car to overheat. For this and other very important reasons, we now realize that AC ductwork doesn’t belong in a typical vented attic. After 50 years of installing AC ducts in the wrong place, why are we just realizing this now? First a little history lesson...

AC ducts in a vented attic.

In 1947 mass-produced, low-cost window air conditioners became possible as a result of innovations by engineer Henry Galson, who set up production lines for a number of manufacturers. That year, 43,000 window air conditioners were sold in the United States. By 1969 more than half of new automobiles were equipped with air conditioning and most new homes were built with central AC. (Ref. National Academy of Engineering. In 1952, in Pompano Beach Florida, the metal plate connected engineered wood truss was invented and patented. The invention marked the beginning of the truss industry, that is still dominating building construction all over the world. (Ref. ) It’s interesting to note that nearly all of the renowned Florida architectural styles pre-date World War II. After costs doubled during the 40’s and early 50’s because of increased cost of labor and materials, many new homes were downsized and simplified.  These modest homes proliferated across the American landscape. It was an extremely significant time in our country’s history with returning veterans from World War II and the Korean War, creating a huge need for simple, secure housing. Tract home communities sprang up across the country, and the suburbs were quickly filled with new homes - all part of the American dream. (Ref. Additionally during this time period, mass-produced concrete blocks became readily available and spurred the growth of Florida concrete industry giants, Rinker and Florida Rock. At the time concrete block seemed like an ideal building material to fill the need for low-cost housing also fueled by population migration into the state. Hence, the now well-known basic Florida construction style developed: slab-on-grade; concrete block walls; and engineered wood trusses for the roof structure. Since most homes in Florida were built without basements, the attic became a convenient place to install the AC ducts. Energy was cheap and air-conditioning was a welcome necessity, so until recently AC ducts have been going into a typical attic and few builders and designers ever considered otherwise. There was a brief interest in increased energy efficiency after the OPEC oil embargo of the 1970’s, but it quickly faded as the affluence and growth of the American economy influenced the purchasing decisions of home buyers and builders. In another post, I’ll discuss how this same affluence has degraded building performance and brainwashed the consumer into comparing homes using cost-per-square-foot analysis.

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