What is a common characteristic of the secondary air in venting systems?

A common characteristic of secondary air in venting systems is that it reduces carbon monoxide concentration. Secondary air is often introduced into the combustion process to ensure that there is sufficient oxygen for complete combustion. By facilitating better combustion, it helps to minimize the production of harmful byproducts, including carbon monoxide. When there is adequate secondary air, the combustion process becomes more efficient, leading to lower emissions of pollutants.

This aspect is crucial in residential and industrial applications, where ensuring safety from carbon monoxide exposure is paramount. Properly designed venting systems utilize secondary air to enhance the overall effectiveness of the combustion process, contributing to a safer and cleaner environment. The other options do not capture this critical function of secondary air in venting systems.