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After a few brands of thermostats that went back to the stores I have discovered a problem with most smart thermostats.....The electronics produce heat. This is aggravated by using radio transmitter to talk WiFi or any other protocol.
You say...just adjust the calibration to compensate? Well that is what the manufacturers do, and also what causes the problem.
Here is an example. Your room is at 72F = 22C, but the electronics in your stat heats the sensor up a few degrees to 75F = 24C.
The QA tech in the factory saw this and adjusted the stat sensor to read 72F or 22C.
So you take it home and mount the new beauty on your wall, and set all the settings to where you want. It reads 72F or 22C and you are comfortable.
Now your HVAC cuts in and the slight breeze in the room hits the thermostat. The same thing can happen from an open door, leaky windows, internal wall draughts, or a ceiling fan. That very slight heat discussed above, from the electronics gets blown away somewhat, and the senor returns to it's rightful place, with the bad calibration now showing 75F of 24C.
But the actual room temperature hasn't changed...!
Now your thermostat does it's job and turns on the HVAC to cool or heat the room. That's it's job. Now you are cold or too hot and adjust the thermostat setpoint.
But it doesn't stay. The breeze stops later and now you feel too much the opposite and wonder why you have to adjust the setpoint back to where it started.
It the stat doing it's job? NO! But most people have no idea what is going on and either, they are insensitive to heat changes (and paid $340 for a stat??? duh), they try to ignore it, or they take it back to the store and install their old not-too-smart thermostat and forget all the new-age hype.
I have found TekMar thermostats not too bad for this, Venstar ColorTouch T7900 units extremely affected , Honeywell TH7950WF somewhat affected, and ecobee3 quite good for this. However the ecobee3 has another sensor display wandering problem where they use the display register to fudge the cycle compensation, forcing it to cycle on what then appears to be a finer response resolution.