Infrared Thermometer Gun Guide – How It Works, When to Use It and Accuracy Explained

Posted by ZOYI UK 11/27/2025 12:05:55 Comments 0

Introduction: What Is an Infrared Thermometer Gun?

An infrared thermometer gun—often called a temperature gun, IR thermometer or laser thermometer—is a handheld device used to measure surface temperature without contact. It detects infrared radiation emitted from an object and converts it into a temperature reading. This makes it ideal for measuring hot, moving, hazardous or inaccessible surfaces safely and instantly.

IR thermometers are widely used across industries: HVAC technicians measure air vent temperatures, electricians check overheating components, mechanics diagnose engine issues, food inspectors verify safety temperatures, and homeowners use them for cooking, heating checks or insulation testing. This long-form guide explains how infrared thermometer guns work, how to use them properly, and how to get accurate readings every time.

How an Infrared Thermometer Gun Works

All objects emit infrared energy (heat). The hotter an object is, the more infrared radiation it emits. Infrared thermometers use sensors to detect this radiation and convert it into a temperature value displayed on screen.

Key Component: The Thermopile Sensor

The sensor absorbs IR energy through the lens and converts it into electrical signals. The thermometer’s processor calculates the surface temperature based on these signals.

Laser Pointer – Only for Aiming

The laser dot does not measure temperature. It simply helps you aim at the surface being tested.

What an Infrared Thermometer Measures

Surface temperature
Temperature differences between areas
Hotspots and cold spots
Overheating components

IR thermometers do not measure:

Internal temperature
Air temperature (with accuracy)
Reflective metal surfaces (without adjustments)

Distance-to-Spot Ratio (D:S) – Why It Matters

The D:S ratio determines how large an area the thermometer reads based on how far away you hold it. For example:

12:1 ratio means at 12 cm distance, you measure a 1 cm area
20:1 ratio means more accuracy at a distance

The higher the ratio, the more precise the reading from farther away.

Common Ratios

12:1 (standard household use)
16:1 (professional HVAC & electrical)
20:1 – 30:1 (industrial and long-range applications)

What Is Emissivity and Why It Affects Accuracy?

Emissivity is a material’s ability to emit infrared energy. Different materials have different emissivity levels.

Most non-metal surfaces have high emissivity (0.90–0.98)
Shiny metals have low emissivity (0.20–0.40)

Adjustable Emissivity

Professional IR thermometers allow you to set emissivity manually for higher accuracy.

Fixed Emissivity

Budget models usually use a fixed emissivity of 0.95, suitable for most surfaces except shiny metals.

How to Use an Infrared Thermometer Gun (Step-by-Step)

Step 1 — Turn On the Thermometer

Most models auto-power on when the trigger is pulled.

Step 2 — Aim Using the Laser

Point the laser at the centre of the area you want to measure.

Step 3 — Hold at the Correct Distance

Use the device’s D:S ratio to ensure accurate measurement.

Step 4 — Pull the Trigger

The device will instantly display the surface temperature.

Step 5 — Take Multiple Readings

Especially important for large surfaces or heat-sensitive areas.

Applications of Infrared Thermometer Guns

1. HVAC & Ventilation

Check heating and cooling system performance
Measure supply/return air vent temperatures
Troubleshoot airflow problems

2. Electrical Work

Identify overheating breakers
Check switchgear temperature
Spot loose or overloaded connections

3. Automotive Diagnostics

Test radiator and cooling system
Inspect brake disc temperature
Check exhaust components

4. Home Use

Check insulation efficiency
Find heat leaks around windows/doors
Measure cooking surface temperature

5. Industrial & Manufacturing

Monitor machinery temperature
Check conveyor systems
Verify thermal processes

6. Food Safety

Check pan, grill and oil temperature
Verify safe holding temperatures

Tips for Accurate Infrared Temperature Readings

Use the correct D:S distance
Avoid reflective metal surfaces
Allow device to acclimate to ambient temperature
Take multiple measurements
Adjust emissivity for complex materials
Ensure the lens is clean

Common Mistakes to Avoid

1. Measuring Shiny Metal Incorrectly

Stainless steel, chrome and aluminium require emissivity adjustment or tape coating.

2. Measuring Through Glass

The thermometer reads the glass surface, not behind it.

3. Holding the Device Too Far Away

Increases measurement area and reduces accuracy.

4. Using in Steam or Dusty Environments

IR energy is scattered, leading to false readings.

5. Expecting Body Temperature Accuracy

Standard IR guns are not medical devices.

Infrared Thermometer vs Traditional Thermometer

Each has advantages: