Penn Electric Tem-Clock Thermostat

This thermostat has a Type 772 Tem-Clock timing apparatus with a T-41 electric switch that was made by General Electric for the Penn Electric Switch Company around 1938. The timer could be set for an AM and a PM temperature, or be turned on automatically when the thermostat hit a certain temperature.

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.

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