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Thermostats track temperature conditions to manage heating, cooling, or exhaust ventilation. When the monitored air reaches a set threshold, the thermostat opens or closes electrical contacts to protect equipment or maintain target temperatures.
Specifications
- Part number: 18781
- Brand: Gaylord
- Part type: Thermostat
- Height: 1 in / 2.54 cm
- Length: 18.25 in / 46.36 cm
- Width: 6.35 in / 16.13 cm
- 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.
How the Thermostat Works
A thermostat reads temperature changes in its operating environment. Depending on how it is installed, it can cycle equipment on or off to protect system components or maintain safe ventilation.
Most control thermostats rely on low-voltage signals, though some systems use line voltage. Knowing your system type is essential so the electrical switch ratings align properly.
Dimensions and Physical Specifications
Replacing an exhaust duct or system thermostat requires matching the physical footprint so the assembly mounts securely in place. The dimensions for part number 18781 are listed below.
- Height: 1 in / 2.54 cm
- Length: 18.25 in / 46.36 cm
- Width: 6.35 in / 16.13 cm
Confirming a Proper Match
Before replacing an old part, verify that the stamped part number matches exactly. In addition to physical dimensions, verify the control type and wiring requirements of your existing setup.
Pay close attention to whether your equipment requires low voltage or line voltage wiring, as mixing them will cause equipment damage or electrical failure.
- Voltage: Check whether your setup uses 24 V control power or line voltage.
- System compatibility: Confirm system type, such as gas, electric, or heat pump.
- Stages: Match the heating and cooling stages your equipment requires.
- Wiring: Check if your setup requires a C wire or specific terminal connections.
Signs of Failure and Safe Replacement Steps
When a thermostat fails, it may fail to close contacts when heat rises, or it may stay open continuously, shutting down the equipment. Follow safe wiring steps whenever installing a replacement.
- Turn off electrical power to the equipment at the breaker panel or service switch.
- Verify the power is fully off using an electrical test tool.
- Take a clear photo of all wiring connections showing which wire attaches to each terminal.
- Disconnect the wires and remove the mounting hardware holding the old thermostat.
- Mount the replacement unit in the same orientation and transfer wires one at a time to the matching terminals.
- Restore electrical power and test the system for normal operation.
Read your old part
- Locate the identification stamp or label on your existing thermostat housing.
- Verify that the part number reads 18781.
- Confirm the brand marking matches Gaylord.
- Measure the existing part to confirm it matches 18.25 in / 46.36 cm in length, 6.35 in / 16.13 cm in width, and 1 in / 2.54 cm in height.
- Compare the terminal design and mounting holes with your original unit before wiring.
When to call a pro
If you are unsure how to test electrical circuits, cannot match the wiring layout, or feel uncomfortable working around electrical controls, stop immediately. Hire a licensed HVAC technician to inspect your system and perform the installation safely.
Questions
What voltage does this type of thermostat usually use?
Most central systems use 24 V control thermostats powered by a transformer. Other setups, such as baseboard heaters, run on line voltage. Always verify your equipment voltage before working on wiring.
Why is it important to take a photo of the wires before removal?
A clear photo shows which wire connects to each letter or terminal mark. Moving wires one at a time according to your reference photo prevents wiring errors that could damage the system.
Can I bypass this thermostat to keep equipment running?
No, you should never bypass a thermostat, limit switch, or safety control. Bypassing controls can cause severe equipment damage, electrical failure, or fire hazards.
Related part numbers
- 18782Thermostat, GaylordSame brand and type
- 11930Thermostat, GaylordSame brand and type
- 300701Hi-Limit Thermostat, ClevelandSame part type
- 1053-00004-00Thermostat, FetcoSame part type
- 10283Relay Reference, GaylordSame brand
- 369801Thermostat, LincolnSame part type
- 1053-00003-00Thermostat, FetcoSame part type
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