Carbon monoxide (CO) is an odorless, colorless, and toxic gas which is a byproduct of incomplete combustion. For HVAC technicians who work on combustion equipment like furnaces, water heaters, and boilers as part of their job, CO is occupational hazard. CO can also threaten the health and safety of people who live and work near combustion equipment which emits excessive amounts of the gas into the ambient air.

Handheld CO meters are great tools for protecting both HVAC pros and the customers they serve. By detecting and measuring the concentration of CO in the ambient air, these handheld devices can quickly alert a technician to an unsafe level of CO present in the immediate area. CO concentrations higher than normal outside air, but still below dangerous levels can indicate an exhaust gas leak, or inefficiently running combustion equipment—both of which require repairing.

ET110 Overview
The ET110 from Klein Tools is one such meter, with its major features designed to help present critical CO measurements and alerts in multiple ways:

• Alarms comprising audible and visual indications when the short-term exposure limit (STEL) CO concentration (200 ppm) and OSHA/NIOSH 8 hour exposure limit level (35 ppm) are detected.
• Backlit monochrome LCD display with the CO ppm readout right in the center, with large digits for clear readings
• A bright dual-color indicator light which glows green when no CO is detected, and flashes red when CO levels exceed 35 ppm.
• A CO measurement maximum limit of 1000 ppm

Other helpful features include a battery-saving automatic shutoff after 20 minutes without usage, air temperature measurements in both Celsius and Fahrenheit, zero-calibration automatically performed at every power-on, and the ability to withstand a drop from a one-meter height.

The four AAA batteries required to power the meter are included with purchase, along with a pouch for storage.

A Closer Look
The electrochemical sensor which directly detects and measures the CO in the air is housed within a small protrusion on the end of the meter, and not on the end of a long bendable neck like those commonly found on combustible gas leak detectors. The reason for this is simple: CO meters like the ET110 aren’t designed to pinpoint the source of a CO leak, but instead to notify all those nearby the amount of CO in the air they’re breathing. CO meters are not for troubleshooting, but for safety.

Speaking of the CO sensor, Klein Tools claims a 5 year expected lifetime for it. Given that the sensor isn’t user replaceable, that long life expectancy is a welcome feature.

Let’s talk more about the ET110 as a CO measurement device. Klein Tools gives the response time for the meter to display 90% of the true CO concentration (referred to as “T90”) as under 60 seconds. The specified resolution for CO measurement is 1 ppm, with a measurement repeatability of +/- 3%. Taken together, this means the ET110 is rather well suited for checking rooms and general areas of combustion equipment for CO, since those levels don’t usually change very rapidly and a tech’s actions aren’t tied to specific CO numbers (e.g. a reading of 32 ppm vs 34 ppm won’t determine whether or not a tech initiates a repair).

This CO handheld meter also includes buttons which display basic CO measurement statistics. The MAX/AVG button allows the tech to cycle through the maximum, minimum, and average values.

The operating temperature range (32°F/ 0°C to 122°F / 50°C) of the ET110 should cover most combustion equipment servicing scenarios, but the RH limit of <85% might present a problem in very humid climates. When it comes to storing this meter, you shouldn’t leave it in your truck if you work in either very hot or very cold climates, as the storage temperature range is only 23°F to 131°F (-5°C to 55°C).

In addition to the CO zeroing during power up mention above, the Klein Tools ET110 features another automatic routine: a 3 minute long diagnostic self-test (initiated by pressing the SET button after the unit powers on), which Klein recommends performing after every 24 hours of usage.
    
Klein Tools has a reputation for high-quality, durable, and eminently useful tools. The ET110 handheld CO meter is no exception. This meter can help protect your safety on the jobsite, as well as the safety of the customers.