One of the most common emergency calls we get in regards to HVAC systems is that our customers smell gas coming from the system. This is an issue that should never be ignored and should always be taken very seriously. A gas leak can cause carbon monoxide poisoning, but it could even be so much worse than that. Although rare, a gas leak can start a fire or cause an explosion. Usually the first sign of a gas leak is the smell of rotten eggs—a scent that gas companies add to gas lines so you’ll be able to detect otherwise odorless gas.