How do I calibrate a honeywell ct87 thermostat?

There is a special tool for that purpose. It is available at local supply houses that sell Honeywell thermostats. Follow the instructions that come with the tool.

There is a special tool for that purpose. It is available at local supply houses that sell Honeywell thermostats. Follow the instructions that come with the tool.

Thanks for the reply hvac1000. The hardware where I bought the thermostat didn't have a clue about re-calibrating it. It's also funny that the honeywell site does not mention how to do it. I will look around for the tool that you spoke of .Thanks again,smarthog1

((It's also funny that the honeywell site does not mention how to do it))

In most cases it is never necessary to do it. Many times the hole in the wall is not caulked in where the wires pass through and that allows cold air to put the thermostat in what seems like a out of calibration situation. Naturally caulking the hole tight or using perma gum or duct seal to close the hole is never followed in the install directions which causes the problem to start with.

BTW you might also check for level on the subbase since that can also put the thermostat out of calibration OR you might also check to be sure the heat anticipator is adjusted correctly which will also cause the unit to run to long or to short of a time. Here is some help for the situation

http://customer.honeywell.com/techlit/pdf/69-0000s/69-1552ef.pdf


Recalibration
The T87F is accurately calibrated at the factory under
Controlled conditions and recalibration is not necessary. If
It appear that the thermostat is out of calibration:
1. Make sure the thermostat is level and not subjected
To radiant heat from the sun, radiators, or
Appliances.
1. Remove the thermostat cover ring to observe the
Mercury switch action.
2. After a five- or ten-minute off period (with thermostat
Setting below room temperature), slowly raise
The setting until the switch just makes contact. If
The thermometer pointer and setting indicator have
The same reading the instant the switch makes, no
Recalibration is necessary.
3. If recalibration is necessary: turn the setting dial a
Few degrees above room temperature and remove
The cover.
4. Slip the 104994 Calibration Wrench (ordered separately)
Onto the hex under the bimetal coil and,
Holding the dial firmly, turn the hex clockwise until
The mercury breaks contact. See Fig. 6.
5. Turn the dial to a low setting so the thermostat
Loses the heat it gained from hands and its own
Operation. Wait at least five minutes.
6. Slowly turn the dial until the pointers have the
Same reading.
7. Firmly holding the dial from turning, carefully turn
The hex counterclockwise until the mercury switch
Slips to the heating contact end of the tube.
8. Recheck the calibration, select the desired temperature,
And replace the cover.
NOTE: When the T87F provides cooling control, calibration
For heating automatically calibrates for
Cooling.

Pic of calibration nut and tool on page 7

http://mas0000.dealerstack.net/T87F_Product_Data.pdf


104994 part number this link cheap at 1.10

Quality Heating and Cooling Supply - Search Results (http://www.qualityhtg.com/q2/searchresults.asp?Category=TOOLS)

hvac1000 the t87f is different than the ct87 in that the ct87 does not use a mercury switch. I ended up taking it back to the store where I bought it and they replaced it. The replacement works just fine.
Thanks for the info,smarthog1



Recalibration
The T87F is accurately calibrated at the factory under
Controlled conditions and recalibration is not necessary. If
It appear that the thermostat is out of calibration:
1. Make sure the thermostat is level and not subjected
To radiant heat from the sun, radiators, or
Appliances.
1. Remove the thermostat cover ring to observe the
Mercury switch action.

WOOPS you are correct. Yours only has the E and F switch to adjust for the install. This is what happens when you get old like me. I always keep thinking of the older thermostat numbers especially when someone asks about a adjustment. Glad you got it replaced.