Chronotherm III Calibration?

There are no bias adjustments for temperature on the Chronotherm III.

Most thermostat theremometers can be calibrated, either in program or by a screw if it is spring type, but you need an accurate source most I see are 1-3 degrees off. A taylor probe style digital is usualy accurate. I had several older mecury bulb Chronotherms , all I could calibrate behind the thermometer. Calibrating the thermostat took a special thin wrench.

Sometimes, if thermostat is just above furnace room and if furnace room has leaks in vents that makes furnace room much warmer, and if heat can travel where thermostat wires are, it can affect thermostat temperature readings.

Could you try to insulate hole behind the thermostat and see if this helps.

Regards,

I appreciate your reply. Thanks! But if your theory were true, wouldn't the thermostat on the wall read HIGHER than one on a nearby shelf? The wall the thermostat is on is in the middle of the house. (The other side of the same wall is another room.) Little chance for a draft or creeping heat from within the wall being the cause of the discrepancy.

Also, the thermostat is not mounted above the furnace room, nor on the same wall with any heat vents or air return vents.

- Earl

The Honeywell Chronotherm III electronic thermostat uses a logritmitc program [Adaptive Intelligent Recovery® control brings the room temperature to temperature setpoint at the programmed time, maximizing comfort and energy savings.] "anticipate" the need for cooling or heating (as the case maybe.) Sometimes the thermostat will show a different setting & temperature because it is compensating using the programming set up by Honeywell. You can defeat the logritmitc program. Call your local HVAC technician to change the Adaptive Control Setting or turn it "off."

This feature came out around 1980 with the first T8600 series and was meant to bring the heating on earlier than the program was set for so, AT the time the thermostat was told to be a certain temperature, it would be, not that it 'came on' at that time. (Mostly an advantage for heat pump use.)

I had a similar situation though not as severe as yours. My two readings were about 2-3 degrees apart. However, it turned out the difference was attributed to the location of the other thermometer. When I place it directly on the wall next to the thermostat and let it sit there for a few hours, guess what? The two agreed on the temperature. Previously, I had them placed close near one another but apparently, "close" was not close enough.

Jay M Hillsboro, VA USA

replying to jMon, statesideqsod wrote: Yes I agree. After many hours of placing my Taylor thermometer on top of the thermostat the 2 readings got pretty close. I would say less than a degree difference. Also make sure the Chronotherm has fresh batteries. Change them at least twice year.