First, before we go farther, we want to stress that natural gas furnaces are not “risky” devices to have in your home. They aren’t ticking time bombs that will eventually become hazardous, and they aren’t something to worry about each time one comes on. If they were any of these things, they would never be allowed into homes in the first place. The modern gas furnace is built with a high priority on safety.

However, burning natural gas—as with burning any combustible energy source—can create dangers without the proper precautions. The company that manufactured your gas furnace already took most of the major precautions. You’ll need to take a few of them yourself to ensure your furnace operates at the highest levels of safety. Specifically, you want to watch out for this malfunction: a cracked heat exchanger.