Where Is the Calibration Screw on a Thermostat?

If you’ve been setting your home’s thermostat and it just doesn’t seem to match the actual room temperature, it might be time for an accuracy check, and possibly an adjustment. If you’d prefer a certified professional to handle the job, call us today at Christian Heating, Cooling, Plumbing & Electrical. Otherwise, let’s walk through where you’ll commonly find the calibration screw, or the equivalent adjustment, and how you’ll know if you need it.

What the calibration screw does

On many older or mechanical thermostats, a small calibration screw is built into the internal mechanism. Its purpose is to fine-tune the thermostat’s temperature reading so that the device activates your heating or cooling at the correct ambient condition. If the thermostat reads, say, 70 °F when the room is actually 73 °F, the screw allows you to shift the reading so the system behaves as expected.

In more modern digital or smart thermostats, there may be no physical screw; instead you’ll find a “calibration”, “temperature offset” or “display adjustment” option inside the settings menu.

Locating the screw or adjustment point

Here are common places to look:

• First, turn off the power to the thermostat (either at the device or at the breaker). This prevents accidental activation of your HVAC system while you work.
• Remove the thermostat cover. On older analog models, this typically exposes the internal bimetal coil or mechanism where a small screw will be mounted centrally on a curved piece of thin metal.
• On digital thermostats: you may not find a physical screw. Instead look for menu options like “Temp Offset,” “Calibration,” or similar.
• Also check that the thermostat’s mounting base is level. On older pneumatic or mercury-tube types a tilt or unlevel base can affect accuracy.

How to recognise if you need to adjust it

Before you locate the screw, make sure adjustment is necessary. Some signs include:

• The temperature reading on the thermostat consistently differs by more than 2–3 °F from a reliable thermometer placed nearby.
• Rooms are noticeably too warm or too cool compared with what the thermostat setting says, even when the HVAC system runs normally.
• Energy bills or system run-times have increased without a clear change in setting or equipment, meaning your thermostat might be triggering the system at the wrong time.

Typical locations of the screw by thermostat type

• Analog / mechanical thermostats: The calibration screw will often be located behind the front plate, mounted on or near the bimetal coil. You’ll need a small screwdriver.
• Mechanical thermostats with mercury switch or pneumatic type: These may rely less on a screw and more on leveling or other internal adjustments (like a heat-anticipator lever).
• Digital and Smart thermostats: No physical screw; calibration is done via software settings. The “calibration screw” concept doesn’t apply. In many cases, if the display is off by several degrees regularly, replacement of the thermostat may be more cost-effective than adjustment.

Why this matters

When your thermostat isn’t calibrated correctly, your entire HVAC system can be thrown off. It may run too long, too often, or fail to reach comfort levels. That means greater wear on equipment, higher energy usage, and reduced comfort. Proper calibration (or replacement when needed) helps maintain accuracy, efficiency, and system longevity.

When to call a professional

If you remove the cover and don’t find a calibration screw, or if you don’t feel comfortable working inside the thermostat, contact a professional technician. With newer systems, improper adjustment or wiring can lead to system issues beyond the thermostat alone. At Christian Heating, Cooling, Plumbing & Electrical we can inspect the thermostat, check wiring and sensor placement, and ensure your overall HVAC system is performing correctly.

Need Help? Call Christian HVAC!

If your thermostat is giving you inconsistent readings, causing discomfort, or seeming to drive up costs, locating and adjusting the calibration screw (or performing the equivalent software adjustment) could solve the problem. But if you’d rather leave it to an expert, our team at Christian Heating, Cooling, Plumbing & Electrical stands ready. Reach out today for a thermostat inspection and calibration check, and keep your home comfortable and efficient.