First double-glazed windows
Thermopane, Charles D. Haven
first first
United States (Milwaukee)

The first double-glazed windows (also known as insulating-glass windows) were developed by American refrigeration engineer Charles D Haven in the early 1930s. Instead of a single pane of glass, Haven's "Thermopane" system had two glass panels separated by an air gap and sealed around the edges with rubber strips. The air between the panes was dehumidified to prevent condensation forming on the inside of the glass. Haven announced his invention in the Architectural Record in 1932 and filed a patent for the design on 12 October 1934.

Secondary glazing, often called "Storm Windows", has been around for centuries, but lacks the sealed air gap that is the defining feature of modern double-glazing. The lack of a seal means that condensation and convection currents can form in the gap between the two layers of glazing, greatly reducing their insulating effectiveness.

The Libbey-Owens-Ford (LOF) Glass Company set up a partnership with Haven in the late 1930s, creating a subsidiary to mass-produce the sealed units. The first commercially-available double glazing was introduced to the North American market in 1938, but was withdrawn the following year due to frequent sealant failures (which led to condensation).

Following this failure, Haven and LOF engineer John Hopfield developed an improved system with improved seals and chemical desiccants. They patented it in 1941, but wartime manufacturing constraints delayed Thermopane's reintroduction to the North American market until 1946.

The first major architectural project to integrate double-glazing was the John Hancock Building in Boston (today called the "Old John Hancock Building" to differentiate it from the 1976 skyscraper of the same name). This structure used 16,205 Thermopane units as part of a design that also incorporated a comprehensive air conditioning system.