The History of the Thermostat – Short #267

In this short podcast, Bryan gives another history lesson and goes over the history of the thermostat.

Before 1883, automatic temperature control simply did not exist; we shoveled fuel into the furnace and opened windows. If a room got too hot in a commercial building, the janitor would go downstairs to choke the draft damper; this person was responsible for manually controlling comfort.

Warren S. Johnson, a Milwaukee-based college professor, sought to do something about his classroom’s sweltering heat. He created a pneumatic thermostat that mounted to the wall, sensed temperature, and used air pressure and mechanical systems to control dampers. This invention grew in popularity, and he founded Johnson Controls.

Compressed air ran entire HVAC networks by adjusting dampers and valves before electricity went mainstream. Engineers experimented with bi-metallic strips, which could open or close an electrical circuit based on temperature changes, which made thermostats smaller and cheaper. Honeywell came on the scene by hiring industrial designer Henry Dreyfuss, who invented the mercury thermostat: the T87 round thermostat. When the bimetal coil tilted, mercury rolled from one end to the other to complete or open the circuit. These thermostats had a heat anticipator, which kept them from overshooting the temperature. Unfortunately, when these thermostats were disposed of, the mercury polluted the environment and affected the central nervous system.

The digital thermostat came on the scene to replace the mercury thermostat, which led to the development of the Nest smart thermostat. However, all this time, comfort has been associated with the number on the thermostat; smart comfort controls that learn our routines and monitor dew point, relative humidity, and IAQ are the next step to create true comfort and health.

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