Friday, July 20, 2007

Short Take: Hysteresis in RTH7500

Frequently asked question with a very vague answer - what is the hysteresis (a.k.a. dead band) of my thermostat?

For Honeywell RTH7500, the measured (therefore not exact) typical value is about 1°C (about 1.8°F) - for the sensor located in the room behind the wall where the thermostat is.

Worst observed value is 2.5°C (about 6.3°F) - for the sensor located on the first floor (the thermostat is at the second) - this is not actually a property of the thermostat, but rather an indication of how badly the airflow was designed.

Another question - can hysteresis be controlled in RTH7500? The answer is: probably not.

If it can, there's no way to do it that is described in the documentation that is sold with the thermostat (yes, I found the manual, feel free to ask me what those numbers mean).

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