The CO91 is used to check ambient CO levels, find leaks along flue pipes, or measure CO concentration in flue gas from furnaces or residential combustion appliances. With a link to the optional infrared printer, results can be printed to document test results, including the date and time. Perform adjustments to the appliance, and then recall the highest level of CO with the CO Max function. With the temperature function you are able to test register outlet temperatures, or monitor stack gas temperature. Three year limited warranty.