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Honeywell T109 Wind-Up Acratherm Brand Thermostat

Honeywell T109 Wind-Up Acratherm Brand Thermostat

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The Minneapolis-Honeywell Regulator Company in Minneapolis, Minnesota made this model T109 Acratherm thermostat around 1936. The Acratherm was one of Minneapolis-Honeywell’s introductory brands, selling for $9.00 in 1936. It included Honeywell’s “accelerator” that anticipated temperature changes before they happened, speeding up the heating system to maintain the current temperature. The lower knob contained a 12-hour mechanism allowing the home owner to set a temporary lower temperature for up to 12 hours, with the heat kicking on whenever the home owner wanted.
The Acratherm was formerly made by the Time-O-State Controls Corporation of Elkhart, IN, which Honeywell acquired in 1934. Acquiring complementary companies was a part of Honeywell’s history since 1927 when the Minneapolis Heat Regulator Company merged with Honeywell Heating Specialties to become the Minneapolis-Honeywell Heat Regulator Company.
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 the 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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overall: 5 3/4 in x 2 1/2 in x 2 1/4 in; 14.605 cm x 6.35 cm x 5.715 cm
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Work and Industry: Mechanical and Civil Engineering
Domestic Furnishings
Engineering, Building, and Architecture
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Exhibition Location
National Museum of American History
Data Source
National Museum of American History
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