Penn Electric Switch Company Thermostat

Albert Penn of the Penn Electric Switch Company in Des Moines, Iowa invented this Type B thermostat in 1930. His invention was given patent number 1,867,756 on July 19, 1932 and describes a room thermostat that operates via an electric circuit controlled by a thermostatic metal bar. A thermostatic metal bar (or bimetallic strip) is used to sense temperature changes and move accordingly. The bar would essentially move one way when the temperature dropped, and another when the temperature rose. As the bar moved, it would close the circuit that turned the furnace on or off, depending on the thermostat’s setting. This “Type B” thermostat was more conventional than the Type AA Penn thermostat seen in objects 2008.0011.14 that was controlled by a temperature actuated bellows element. This thermostat has an embedded thermometer and a metal slider sets the thermostat.
The ubiquity of thermostats in 21st century homes shrouds the decades of innovation, industrial design, and engineering that went into making them an everyday object in almost every home. In the early 20th century, a majority of American households still heated their homes with manually operated furnaces that required a trip down to the basement and stoking the coal fired furnace. Albert Butz’s “damper-flapper” system was patented in 1886 and allowed home owner to set the thermostat to a certain temperature which would open a damper to the furnace, increasing the fire and heating the house. Progressive innovations allowed for the thermostats to use gas lines, incorporate electricity, turn on at a set time, include heating and cooling in one mechanism, and even connect to the internet.
overall: 5 1/8 in x 2 in x 1 1/2 in; 13.0175 cm x 5.08 cm x 3.81 cm
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Work and Industry: Mechanical and Civil Engineering
Domestic Furnishings
Engineering, Building, and Architecture
Object Project
Exhibition Location
National Museum of American History
Data Source
National Museum of American History


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