March 18, 2021

Furnaces that burn natural gas are the most common type of home heating found in America. Consisting primarily of methane, natural gas has no odor in its unprocessed state. Nevertheless, many homeowners experience smells—such as rotten eggs—that are potentially related to their furnace and are concerned about it.

Are gas-related smells to be expected with a gas-burning furnace? The answer is not as simple as a yes or no, however, since smells in certain scenarios are to be expected while others are not.

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The Smell of Natural Gas

As mentioned in the introduction, natural gas has no odor in its natural state. That could prove quite dangerous in residential environments, so utility companies mix in the chemical mercaptan. Mercaptan is sulfur-based, and it creates a smell that many people associate with rotten eggs. Mercaptan is harmless to humans and pets, and the unsavory smell simply serves as a warning of gas leakage. But it can crop up at other times as well, and smelling it does not necessarily mean that you have a gas leak.

Is There a Gas Leakage?

Let us begin with the most hazardous scenario: a gas leak. It is worth mentioning that gas leaks involving home furnaces are uncommon, but there is certainly the potential. If the smell of gas is strong and persistent, it is possible that you have a gas leak. At this point, you have to make a judgment call. Is the danger of combustion imminent? If so, leave the home immediately. If not, turn off the valve to the gas source, and open any windows that can be opened quickly and easily. Then, depart the home. Once you are outside and at a safe distance from the home, call your local fire department. Next, call your gas company. Once the issue has been identified, it may be necessary to call an HVAC technician. Do so as soon as possible. Most heating companies provide emergency services for such situations.

Carbon Monoxide Detection

Let us dispel a prevalent misconception: carbon monoxide detectors do not detect gas leaks. If you would like gas leak detection added to your heating equipment, dedicated leak detectors are available that can identify even relatively minor seepage. Nevertheless, carbon monoxide detection is important, and most residential building codes required CO detectors to be installed alongside gas-burning furnaces. But keep in mind that you cannot smell CO. It is a byproduct of an incomplete burn, which can occur due to various furnace malfunctions. As CO levels increase, CO poisoning occurs. This will eventually lead to suffocation, and CO is also combustible and can lead to a fire in the home.

Running Your Furnace for the First Time This Season

There is a long stretch throughout the year during which your furnace goes unused. What is almost unavoidable during this period is dust accumulating in and on the various components of your furnace. When you run the furnace for the first time in fall or winter, the dust is heated and eventually burns away. The burning dust does not present much of a risk, but what it does do is react with the mercaptan that has been added to your natural gas. You may smell this odor not just near the furnace but coming through the vents. Such smells are perfectly normal and nothing to be concerned about. If the smell lingers, then that can indicate an actual problem. If you would like to avoid these early-season odors, you can do so for the most part by having your furnace and your ducts cleaned. In fact, the ideal scenario is to have a trusted heating technician be the first one to fire up your furnace each season.