Infrared Thermometer Basics & Best Practices

Infrared thermometers have obvious appeal—measuring the temperature of something without having to touch it or even be near it. But before you purchase an IR thermometer, there are some important questions you need to consider and some limitations you should keep in mind.

The first important stipulation is that all ThermoWorks thermometer products except for one are intended for food service, food processing, industrial, scientific and general home use. Our only FDA-cleared thermometer is the WAND™ No Touch Digital Forehead Thermometer. It is an infrared forehead thermometer that uses an algorithm to translate forehead temperatures to oral-temperature equivalents. For more information on using infrared thermometers for health screenings, read this other article with important considerations.

That said, you can rest assured that ThermoWorks IR guns are the best in the business. No matter which unit you select, you can be sure you’ll receive a fast, highly accurate, and ruggedly durable product. Plus, all ThermoWorks IR guns come with warranties against defects in either components or workmanship for added peace of mind.

Why Use Infrared Thermometers?

➤ Take Measurements From a Distance

Infrared thermometers are ideal for taking temperatures that need to be tested from a distance. They provide accurate temperatures without ever having to touch the object you’re measuring (and even if your subject is in motion).

This is ideal when you can’t insert a probe into the item being measured, if the surface is out of reach, or if you have to keep your distance because of high heat. You might use an infrared thermometer to measure objects that are:

Fragile (computer circuitry) Dangerous (gears, molten metal) Impenetrable (frozen foods)

Susceptible to contamination (foods, saline solution) Moving (conveyor belt, living organisms) Out of reach (air conditioning ducts, ear drums)

➤ Infrared Thermometers Measure Surface Temperature

Infrared thermometers are great for checking surface temperature, however, they do not measure the internal temperature of an object.

Infrared thermometers are very fast, typically giving a reading in a fraction of a second, or the time it takes for the thermometer’s processor to perform its calculations. Their speed and relative ease of use have made infrared thermometers invaluable public safety tools in the food service industry, manufacturing, HVAC, asphalt & concrete, labs and countless other industrial applications.

Limitations of Infrared Thermometers

Infrared thermometers can be very useful when used in the right way and put to task in the right applications. However, before you can develop confidence in their ability to give fast temperatures, you need to understand their limitations.

Infrared thermometers:

• Only measure surface temperatures and NOT the internal temperature of food or other materials. An IR thermometer is not a substitute when an instant-read thermometer is needed to measure internal temperatures in foods.
• Require adjustments depending on the surface being measured (See “What is emissivity” below)
• Are not typically thought to be as highly accurate as surface probe measurements of the same surface*
• Can be temporarily affected by frost, moisture, dust, fog, smoke or other particles in the air
• Can be temporarily affected by rapid changes in ambient temperature
• Can be temporarily affected by proximity to a radio frequency with an electromagnetic field strength of three volts per meter or greater
• Do not “see through” glass, liquids or other transparent surfaces—even though visible light (like a laser) passes through them (i.e. if you point an IR gun at a window, you’ll be measuring the temperature of the window pane, not the outside temp).

* Note that in some unique instances, Infrared Thermometers can actually be MORE accurate than a surface probe because surface probes have their own temperature and can affect the surface being measured by coming into contact with it.

Infrared FAQs

➤ Can I check my grill temp with an infrared thermometer?

Yes! However, if you aim an infrared thermometer at a porous surface like a grill or grate, it will factor in the surface temp of whatever surfaces are visible through the holes of the grill or grate when calculating a final temperature for your reading.

How to Measure Your Grill’s Temperature with an Infrared Thermometer

• Place a solid surface like a cast iron plate or skillet on the grill and let it preheat for 5-10 minutes.
• Spray a little cooking oil on the cast iron’s surface to ensure proper emissivity.
• Measure the surface temperature of the plate or skillet with your IR thermometer.

➤ Can I use an infrared thermometer to measure the temperature of my oven?

No. Your infrared thermometer will only measure the surface temperature of the oven’s walls. To accurately measure the temperature of the interior of your oven, use a Pro-Series^® Air Probe secured with a Grate Clip on one of the oven racks. Pro-Series probes are compatible with Smoke™, ChefAlarm^®, and DOT^®. For more information on how to measure the temperature of your oven, see our post Testing Your Oven’s Accuracy. However, you CAN use an infrared thermometer to measure the temperature of a surface in your oven, like a pizza stone or a cookie sheet.

➤ What is emissivity?

All objects radiate or emit electromagnetic energy. Think of light emanating from a lamp, or red glowing embers. “Emissivity” is a measure of a material’s ability to emit infrared energy. It is measured on a scale from just above 0.00 to just below 1.00.

Generally, the closer a material’s emissivity rating is to 1.00, the more that material tends to absorb reflected or ambient infrared energy and emit only its own infrared radiation. Most organic materials, including the byproducts of plants and animals, have an emissivity rating of 0.95.

Emissivity Affects Infrared Readings

Think of a mirror, it reflects nearly all of the energy directed toward it. It will emit the infrared energy from the thermometer as well as its own radiated energy. Because of this, infrared temperature readings from low emissivity materials such as aluminum and stainless steel are not accurate. However, if an aluminum or stainless steel pan is coated in oil (organic material), the pan’s emissivity increases because of the thin film of oil on its surface.

Check your infrared thermometer to see if it has adjustable emissivity settings as a feature. Then check your target material against this ThermoWorks Emissivity Table.

➤ Can I check my meat or other foods for doneness with an infrared thermometer?

Since infrared thermometers only measure surface temperatures, they are not very effective at gauging the doneness of foods. Only traditional probe thermometers can determine the internal temperature of solid foods.

Using an IR Thermometer to Measure the Temperature of Liquids

When using an infrared thermometer with liquids like soups and sauces, be sure to stir vigorously before taking a measurement to equilibrate the temperature in the volume of liquid and more accurately approximate the internal temperature of the liquid. Be aware that steam, even when a liquid is not boiling, can condense on your thermometer and affect the accuracy of your measurements.

➤ Can infrared thermometers see through glass or clear plastic?

Infrared thermometers do NOT “see through” glass, liquids or other transparent surfaces. Even though visible light (like a laser) passes through them—i.e. if you point an IR thermometer out a window, you will be measuring the surface temperature of the window itself.

➤ Do infrared thermometers see through water?

No. Infrared thermometers can only measure the surface temperature of water—even if the laser’s light passes through the water as described above.

➤ What is “spot size,” “spot ratio,” or “distance to target ratio”?

Spot size

The “spot size” of any given measurement is controlled by two variables:

1. The “distance to target ratio” or “spot ratio” of your particular infrared thermometer
2. The distance between your infrared thermometer and the target

Distance to Target Ratio

Typically listed on the thermometer itself, the “distance to target ratio” (DTR) or “spot ratio” tells you the diameter of the “circle” of the surface area an IR thermometer will measure at a given distance.

For example: An infrared thermometer with a 12:1 ratio will measure the temperature of a 1″ diameter circle of surface area from 12″ away, a 2″ diameter circle of surface area from 24″ away, and so on.

➤ Does the angle I hold my infrared thermometer in relation to the object being measured matter?

Yes. Simply put, always try to hold the lens or opening of your infrared thermometer directly perpendicular to the surface being measured. That way the border of the surface area being measured by your thermometer will be a tight circle. When you hold your infrared thermometer at an angle relative to the surface being measured, the area in your “snapshot” will be elliptical and harder to control.

➤ Do I need to clean my infrared thermometer?

Yes! To be accurate, infrared thermometers must be kept free of dirt, dust, moisture, fog, smoke and debris. Always take the time to clean your infrared thermometer after exposure to dirty, dusty, smoky or humid conditions. You should also plan a regular cleaning about every six months. Particular care should be taken to keep the infrared lens or opening clean and free of debris.

How To Clean Your Infrared Thermometer:

1. Use a soft cloth or cotton swab with water or medical alcohol (never use soap or chemicals)
2. Carefully wipe first the lens and then the body of the thermometer
3. Allow the lens to dry fully before using the thermometer

*Never submerge any part of the thermometer in water.

➤ How do I turn the laser on and off?

It depends on the particular model of infrared thermometer you are using. Consult the user’s manual that came with your thermometer for the full range of features and how to use them. This is how to turn the laser on and off with a few of our IR thermometers:

IRK-2: Press the “C/F” button while holding down the trigger. Press again to turn the laser off.

IR-GUN-S: First hold the “Measure” key, then press the “C/F” key for laser function on/off.

IR-IND: First hold the “Measure” key, then press the “Down” key for laser function on/off.

➤ Why am I getting odd readings on shiny metal?

Substances with very low emissivity ratings, like highly-polished metals, tend to be very reflective of ambient infrared energy and less effective at emitting their own electromagnetic waves. If you were to point an infrared thermometer with fixed emissivity at a stainless steel pot filled with boiling water, for example, you might get a reading closer to 100°F (38°C) than 212°F (100°C). That’s because the shiny metal is better at reflecting the ambient radiation of the room than it is at emitting its own infrared radiation.

Adjustable and Fixed Emissivity

Some infrared thermometers (like the Food Safety Infrared) have fixed emissivity settings of (usually of 0.95 or 0.97) to simplify their operation while leaving them suitable for most material surfaces, including almost all foods.

But other infrared thermometers (like the IR-GUN-S, IRK-2, and IR-IND) come with adjustable emissivity settings, so you can more accurately prepare your thermometer for the type of surface being measured, particularly when measuring non-organic surfaces.

➤ Can I calibrate my infrared thermometer myself?

Infrared thermometers can be calibrated for accuracy just like other thermometers. In calibration labs (like the Accredited ThermoWorks Calibration Laboratory at our headquarters in American Fork, Utah), technicians use industrial black bodies (like the IR-500 Portable IR Calibrator) to calibrate infrared thermometers (please contact us at calibration@thermoworks.com or ask for the calibration lab at 1-800-393-6434 or 801-756-7705).

If neither an industrial black body or a comparator cup are available, however, you can do a quick calibration using a properly made ice bath.

Infrared thermometers give incredibly rapid results and are a good solution when a traditional probe thermometer simply can’t get the job done. Whether you need to measure the temperature of ductwork, electrical panels, or the surface of your grill, we’ve got you covered.

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Take a look at some of our top-selling IR thermometers: