Natural gas is a common, efficient, and relatively environmentally-friendly heating option used in many colder parts of the country. While gas furnaces are safe and reliable, they still utilize flammable gas and combustion that can create the potential for safety hazards.
As a result, most homeowners become concerned when their furnace begins making strange noises. Of course, a loud and violent "bang" when your furnace first ignites can be a particularly worrying symptom. This sound often results from a problem known as delayed ignition, and it's not a warning sign that you should ignore.
What's Causing the Noise?
If you've used a gas stove with a dirty burner, you may have already experienced delayed ignition. Instead of the burner lighting immediately, there's a momentary delay followed by a brief (and often frightening) burst of fire before the burner settles back to its normal flame. This brief explosion occurs because of the presence of excess fuel before ignition.
Delayed ignition typically occurs for the same reason in a gas furnace. Something prevents the burners from lighting promptly, leading to an incorrect mixture of fuel and air in the combustion chamber. As the burners finally ignite, this mixture can go off with a loud bang. Depending on the severity of the problem, you may be able to hear it almost anywhere in the home.
The good news is that your furnace is unlikely to explode, but delayed ignition can still cause damage to your equipment. More importantly, it may be a symptom of a much more hazardous condition. If you consistently hear the sounds of delayed ignition, you should stop using your furnace and call a professional for repair.
Why Is It Happening?
There are numerous reasons why delayed ignition can happen. In general, delayed ignition will result from an imbalance in combustion gases or impurities in the mixture. Clogged, dirty, or damaged burners are one typical culprit. As the burner nozzles become clogged, some burners may ignite more slowly than others. When they finally start burning, you'll hear an explosion as the excess gas ignites.
Another potential issue lies with the exhaust flue. Your furnace's air intake and exhaust system are effectively the same. As combustion gases leave through the exhaust flue, the furnace draws in more clean air for combustion. A clog in the exhaust flue can leave old combustion products behind, starving the furnace of fresh air and resulting in an explosion as the first tries to ignite.
Finally, and most critically, delayed ignition can be a symptom of a cracked heat exchanger. A cracked heat exchanger is dangerous and can allow toxic gases to enter your home. Since heat exchanger problems are always a possibility with delayed ignition, it's crucial to rely on an experienced HVAC contractor to inspect any furnace experiencing a delayed ignition issue.
Contact a local heating repair service to learn more.