The heating, ventilation, and air conditioning trade is one of invisible forces and subtle measurements. The HVAC technician does not simply install equipment and walk away; they commission systems, verify performance, troubleshoot failures, and certify that the air being delivered to a building is at the correct temperature, moving at the correct velocity, and—critically—free of dangerous contaminants. Two of the most fundamental measurements that an HVAC technician makes are temperature and carbon monoxide concentration. Temperature is the primary indicator of system performance: the temperature drop across an air conditioning evaporator coil, the temperature rise across a furnace heat exchanger, the temperature of the air leaving a supply register. Carbon monoxide is the silent, odorless, colorless killer that can result from a malfunctioning fuel‑burning appliance—a cracked heat exchanger, a blocked flue, inadequate combustion air, or a backdrafting water heater. The technician who fails to detect a carbon monoxide leak may be the last person to leave the building before the occupants are overcome. The Klein ET05 Digital Pocket Thermometer and the Klein ET110 Carbon Monoxide Meter are two compact, easy‑to‑use instruments designed specifically for the HVAC professional who needs to take these critical measurements quickly, accurately, and reliably. They are not the most advanced or feature‑rich instruments on the market, but they are designed to be simple, durable, and affordable—the kind of tools that an HVAC technician can carry in a shirt pocket and deploy in seconds, without navigating complex menus or consulting a manual. They represent Klein's understanding that the best diagnostic tool is the one that is ready when you need it, that gives you the information you need without unnecessary complexity, and that survives the drops, the dust, and the temperature extremes of the job site.

The Klein ET05 Digital Pocket Thermometer: Wide Range, Fast Response, and a Protective Sheath That Doubles as a Handle


The Klein ET05 is a digital pocket thermometer that measures temperature over a range of ‑40°F to 482°F (‑40°C to 250°C) with a resolution of 0.1 degrees. The sensor is a stainless‑steel probe, 3 inches long, that is suitable for measuring the temperature of air, liquids, and surfaces. The probe is FDA GRAS‑compliant—Generally Recognized As Safe—which means it is constructed from materials that are approved for incidental contact with food. While the ET05 is not marketed as a food thermometer, the GRAS compliance is a reassurance for technicians who may use the thermometer to measure the temperature of potable water or air in food service environments. The probe is housed in a protective sheath that slides over the sensor when the thermometer is not in use. The sheath is open at the sides, which allows ambient air to circulate around the sensor even when the sheath is in place. This design feature enables the thermometer to measure ambient air temperature without removing the sheath—the technician can simply hold the thermometer in the air stream and get a reading, without worrying about the sensor being damaged by contact with a surface. The sheath also doubles as a handle extension when the probe is inserted into a tight or hot location, allowing the technician to keep their hand away from the heat source or the moving parts. The display is a backlit LCD with large, legible digits that are easy to read in dim mechanical rooms, attics, and crawl spaces. The thermometer can display readings in either Fahrenheit or Celsius, selectable by a toggle button. A Hold button freezes the current reading on the display, allowing the technician to capture a measurement and then bring the thermometer to a better‑lit area to read it. A Max/Min/Avg button allows the technician to track the maximum, minimum, and average temperature over a period of time—useful for monitoring a system as it cycles on and off, or for checking the temperature stability of a space over several minutes. The thermometer automatically powers off after 15 minutes of inactivity to conserve battery life. A pocket clip provides convenient storage in a shirt pocket or a tool pouch, and the clip doubles as the battery compartment cover, which means the battery is easily accessible for replacement. The thermometer runs on a single LR44 button cell battery, which is included. The compact size and light weight make the ET05 an ideal tool for the HVAC technician who needs a thermometer that is always within reach, whether they are checking the temperature drop across a coil, measuring the flue gas temperature of a furnace, or verifying the accuracy of a thermostat.

The Klein ET110 Carbon Monoxide Meter: Detection From 0 to 1,000 PPM, Audible and Visual Alarms, and a STEL Alarm for Short‑Term Exposure Protection


The Klein ET110 Carbon Monoxide Meter is a handheld, battery‑powered instrument that measures the concentration of carbon monoxide (CO) in ambient air. It uses an electrochemical sensor, which is the same type of sensor used in professional‑grade CO analyzers and in residential CO detectors. The electrochemical sensor generates a small electrical current when it comes into contact with CO, and the magnitude of that current is proportional to the CO concentration. The ET110 displays the CO concentration on a backlit LCD in parts per million (ppm), with a range of 0 to 1,000 ppm. The display also shows the ambient temperature, which can be toggled between Fahrenheit and Celsius. The meter provides both audible and visual alarms when CO is detected. A low‑level alarm triggers at 35 ppm—a level that is below the threshold of immediate danger but that indicates a potential problem that should be investigated. A high‑level alarm triggers at 200 ppm—a level that requires immediate action to ventilate the space and evacuate occupants. The audible alarm can be muted for situations where silence is required, and the visual alarm—a warning indicator light that blinks green for clean air and red for CO detection—continues to provide feedback even when the sound is off. A particularly valuable feature for the HVAC technician is the STEL alarm. STEL stands for Short‑Term Exposure Limit, and it is a measure of the average CO concentration over a 15‑minute period. OSHA and other regulatory agencies set STEL limits for CO exposure to protect workers from the cumulative effects of moderate‑level exposure over a work shift. The ET110 monitors the STEL and provides an alarm if the 15‑minute average exceeds the safe limit. This is an important safety feature for the technician who is working in a space where CO is present—they may not feel the effects of low‑level exposure immediately, but the STEL alarm ensures that they do not unknowingly exceed the safe exposure limit over the course of a job. The ET110 includes Max, Min, and Average functions that track the CO readings over a measurement session. The Hold button freezes the current reading on the display. A Set button allows the technician to adjust the calibration of the sensor, though the meter is factory‑calibrated and should not require adjustment under normal use. The meter automatically powers off after 20 minutes of inactivity to conserve battery life. It runs on four AAA batteries, which are included, and it comes with a carrying pouch that protects the meter when not in use. The ET110 is not a substitute for a personal, wearable CO monitor that provides continuous, real‑time protection for an individual worker. But for the HVAC technician who needs to verify that a furnace is venting properly, that a gas appliance is not leaking CO into the living space, or that the ambient CO level in a mechanical room is safe, the ET110 provides a quick, reliable, and easy‑to‑use solution.

Klein ET05 and ET110 Specifications


SpecificationET05 Digital Pocket ThermometerET110 Carbon Monoxide Meter
Measurement Range‑40°F to 482°F (‑40°C to 250°C)0 to 1,000 ppm CO
Resolution0.1°F / 0.1°C1 ppm
Sensor TypeStainless steel probe (3″)Electrochemical
FunctionsHold, Max/Min/Avg, °F/°C ToggleHold, Max/Avg, STEL Alarm, Mute, °F/°C Toggle
AlarmsN/ALow‑level at 35 ppm, High‑level at 200 ppm, Audible (mutable) and Visual
DisplayBacklit LCDBacklit LCD
Auto Power OffAfter 15 minutesAfter 20 minutes
Power Source1 × LR44 (included)4 × AAA (included)
IncludedBattery, protective sheathBatteries, carrying pouch


Conclusion: Two Essential Tools for the HVAC Diagnostic Toolkit


The Klein ET05 Digital Pocket Thermometer and the Klein ET110 Carbon Monoxide Meter are not flashy products. They will not generate excitement on tool forums or in trade show booths. But they are, in their quiet, utilitarian way, two of the most essential tools that an HVAC technician can carry. Temperature and carbon monoxide are the two measurements that define the performance and the safety of every fuel‑burning and every air‑moving system that an HVAC professional touches. The ET05 provides a fast, accurate, and convenient way to measure temperature in air, liquids, and on surfaces. The ET110 provides a reliable, easy‑to‑use means of detecting the invisible, odorless gas that can turn a routine service call into a life‑threatening emergency. Both tools are designed with the understanding that the best diagnostic instrument is the one that is always within reach, that gives a clear answer without requiring a manual, and that survives the inevitable drops and bumps of daily use. At their modest price points, they represent exceptional value for the HVAC professional who values accuracy, reliability, and simplicity. They are worthy additions to Klein's growing line of test and measurement tools, and they are products that every HVAC technician should consider carrying.