Monday, August 9, 2010

Honeywell RTH7500: Long Term Verdict

Surprisingly, the most annoying feature of this thermostat turned out to be lack of programmable hysteresis, a.k.a. deadband.

This particular one, installed in this particular location, allows runtimes as short as three bleeping minutes - whereas the time required to get into more or less efficient operating mode is no less than about five minutes for furnaces and about fifteen minutes for an A/C or a heatpump.

Likewise, there is no minimum run time protection (sometimes called short cycling protection).

In other words, this thermostat will make your unit work much less efficiently than it is designed to, and the only way to prevent that is to put the thermostat in a place where the temperature changes very, very slowly - like a closet or a thermally insulated box. Which is not quite that practical.

So, thumbs down, no go.

Likewise, if I ever have to select a thermostat again, I will pay particular attention to presence of programmable hysteresis and minimum run time.

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