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If you are holding an old unit with this number, it controls your comfort directly from the wall. This guide explains what the part specs mean and how to confirm a match safely.
Specifications
- Part number: CT87K1004
- Brand: Honeywell
- Part type: Thermostat
- Depth: 1.09 in; 28 mm
- Dimensions: 3.62 x 2.88 in.
- Height: 3.69 in; 94 mm
- Stages: 1 Heat
- System: No
- Width: 3.69 in; 94 mm
- System: gas, electric or heat pump, as listed
- Stages: heat and cool stages your system uses
- C wire: needed by some models, check yours
From the maker's and parts sellers' listings for this number. Compare them with the label on your old part.
What this thermostat does
A wall thermostat acts as the switch for your home heating. When the indoor air cools down past your chosen setpoint, internal sensors detect the drop. The thermostat closes the circuit to call for warmth from the system.
Once the room reaches the desired temperature, the circuit opens again to shut down the heat. A manual model uses direct adjustments on the dial without digital schedules.
Understanding the part specifications
Matching replacement hardware requires checking physical size and heating stages. The listed specifications for the CT87K1004 detail its exact measurements and system design.
- Stages: 1 Heat
- System: No
- Dimensions: 3.62 x 2.88 in.
- Height: 3.69 in; 94 mm
- Width: 3.69 in; 94 mm
- Depth: 1.09 in; 28 mm
How to confirm a match
To confirm a match, check the heating equipment you have. Look at whether your system is gas, electric or heat pump, as listed for your equipment. Verify the heat and cool stages your system uses, since this part lists 1 Heat.
Also check if your setup has a C wire, which is needed by some models. Central systems often rely on 24 V, but electric baseboards use line voltage. Make sure your system voltage aligns before moving forward.
Signs of failure and safe replacement steps
Thermostats can fail due to loose connections, aging internal switches, or physical damage. You might notice the heating equipment never starts, runs without stopping, or ignores the setpoint dial.
Replacing the unit requires basic electrical caution to prevent equipment damage.
- Turn off power to the furnace or air handler at the breaker panel or service switch.
- Verify the power is off by testing with a meter or ensuring the equipment cannot turn on.
- Remove the cover and take a photo of which wire goes to which letter.
- Disconnect the wires carefully so they do not fall back inside the wall opening.
- Mount the base, reconnect the wires to their matching terminals, and attach the cover before restoring power.
Read your old part
- Remove the thermostat body from its wall plate to access the back casing.
- Locate the printed label or stamp on the plastic housing.
- Confirm the label shows part number CT87K1004.
- Check that your heating setup only requires 1 Heat stage.
When to call a pro
If you are unsure whether your home uses 24 V or line voltage, or if you smell gas near your heating appliances, stop right away. Shut off the system and call a licensed pro to inspect your wiring and equipment.
Questions
What stages does the Honeywell CT87K1004 support?
The CT87K1004 is rated for 1 Heat stage. It is designed for simple heating equipment that does not require multi-stage controls.
What are the dimensions of this thermostat?
This part has dimensions of 3.62 x 2.88 in. Its height is 3.69 in; 94 mm, width is 3.69 in; 94 mm, and depth is 1.09 in; 28 mm.
Do I need to take a picture of the wires before removing the old unit?
Yes, take a photo first. Before you pull the old one off the wall, take a photo of which wire goes to which letter to ensure you wire the replacement correctly.
Can I use this thermostat on a line-voltage baseboard heater?
Most central systems use 24 V thermostats, while baseboard heaters use line voltage. They are not the same, so check your system requirements before choosing a replacement.
Related part numbers
- C7189U1005Thermostat Part, HoneywellSame brand and type
- CT31AThermostat Wiring and Match Guide, HoneywellSame brand and type
- 1053-00003-00Thermostat, FetcoSame part type
- 1053-00004-00Thermostat, FetcoSame part type
- 11930Thermostat, GaylordSame part type
- 46910700Thermostat Specs and Replacement Guide, APWSame part type
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Brand names and part numbers identify the part and show fit. HVAC Fitter is not affiliated with, authorized by, or endorsed by any equipment maker. If you are not sure a repair is safe for you, call a licensed HVAC technician.