Furnace Smells Like Gas When Running? (Know the Danger Signs)

How Often Should A Furnace Cycle In Winter

Because of the affordability of natural gas, it only makes sense that many furnaces are fueled by it. Nearly 62 million American homes make use of natural gas-powered furnaces. Generally speaking, natural gas furnaces are a cheap, reliable way of heating your home.

From time to time, though, you may notice that your home smells like gas when the furnace is running. It could be due to regular emissions or it can be due to the presence of carbon monoxide. No matter what the cause winds up being, calling a professional HVAC technician to take a look is the best option.

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The Most Common Reasons for a Gas Smell

The important thing to note is that a gas smell does not mean that you are in danger. While it certainly could be something like carbon monoxide poisoning, there are also very common causes for that smell that are far less hazardous.

Above all else, the most important thing that you can do is call an HVAC technician when you begin noticing that gas smell. It is always better to be safe than sorry, especially when it comes to the emission of gas in your home.

Start of the Heating Season

One of the more common reasons for smelling gas in your home could simply be due to inactivity. In most climates where a furnace is required, it is dormant for the spring and summer months (and even the early fall).

When you kick your furnace on, all of the dirt, dust, and other impurities that have been sitting in your furnace can start to stir up. That “gas” smell can simply be the furnace burning off all of that accumulated dirt and debris.

This is totally normal, and you can implement a quick fix to alleviate the issue. Simply open up a couple of windows to provide some cross ventilation and you should notice the smell dissipate in short order.

Regular Emissions

You may also notice that your furnace gives off that gas smell well into the heating season. When you can safely determine that it isn’t just dust and dirt burning off, there is actually another regular emission involved.

It is completely normal to note that most gas furnaces give off small amounts of gas when they cycle on. If you are smelling faint notes of gas close to the furnace when a cycle kicks on, you generally have nothing to worry about.

When the problem becomes frequent, though, it could be a potentially dangerous leak. When you notice the gas smell, make note of it and see if it persists over time.

Carbon Monoxide

The other reason that you may be smelling gas emanating from your furnace is due to carbon monoxide. Whenever the fuel in your furnace (gasoline, natural gas, kerosene, and so on) is burned, carbon monoxide is released.

That carbon monoxide is vented out of your home when the gas furnace kicks on. When the furnace is old, the venting system becomes blocked, or the unit is improperly maintained, gas can build up within your home.

Carbon monoxide is also colorless and odorless, called the “silent killer” for a reason. There are two ways to protect your home from carbon monoxide poisoning.

  1. Install carbon monoxide detectors. You should have these in your home already, but if you don’t, now is the time. Carbon monoxide detectors will go off when there is excess carbon monoxide in the air and can mean the difference between life and death.
  2. Have your furnace serviced. Though it may be a little additional cost and time spent, having your furnace serviced is essential. Not only will you protect your home from those dangerous carbon monoxide leaks, but you will also keep the components of your furnace from wearing out and becoming excessively damaged.

Do You Hear Hissing?

Sometimes you may be able to hear a gas leak before you smell it. Generally speaking, you will hear a hissing sound coming from behind a wall or from a pipe. When gas leaks out from a gas line, it makes that hissing sound as the air escapes through the small openings in the gas line.

If you are having a tough time pinpointing the smell, listen for hissing. This can help you identify the origin of the leak and perform a repair immediately or call in an HVAC technician to do the job. The important thing is that you now know where the leak is coming from.

Gas Line Leaks

There may also be a time where you have a gas leak, but it isn’t happening in your furnace. In most cases, the gas lines that run into your home run under your yard. Those gas lines can run directly under vegetation, in some cases.

Should you notice that there is a patch of yellowish, brownish grass that seems to be dying, an underground leak could be the culprit. Even if the leak looks like it is in your yard, it is imperative that you evacuate your home and make the right calls. The leak could have permeated the home without you realizing and create a dangerous environment.

Things You Can Do if You Smell Gas

Trace or faint amounts of gas can be totally normal to smell (as covered above). But smelling it on a regular basis is something to be concerned about. Thankfully, there are a few things that you can do in the even that your home smells of gas.

  1. Cut off spark sources. Should you smell gas in your home, the first thing to do is to avoid lighting matches or eliminate fire sources. Unplug your fridge as the components within can generate a spark when starting. Depending on the severity of the gas issue, even the smallest of sparks can start a major fire or explosion.
  2. Turn off the gas. The next step should be to turn the gas off. Even if there are excess amounts in the home already, stopping the flow of more is always a good idea. If you feel that there is a lot of gas in your home, evacuating the home and calling the fire department, gas company, and heating company is a good idea.
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Related Questions

Can a Gas Furnace Explode?

Technically speaking, it is possible for your gas furnace to catch on fire and even potentially explode. That said, it is a highly unlikely event. Most modern furnaces have safety measures built in to shut off when it detects potential safety issues.

With older units, there could be concerns of explosion in the event of a gas leak, but even those aren’t likely. Update your furnace and provide proper preventative maintenance and you likely won’t have anything to concern yourself with.

How Can I Tell if My Furnace is Dying?

While a gas leak is certainly cause for concern, it could be indicative of a larger issue. That larger issue could mean that your furnace is potentially dying. There are several warning signs that can tip you off but depending on the condition of your furnace, you may have to replace the entire thing.

  1. Lack of heating. The first and most obvious sign that your furnace is dying is that it doesn’t do its job. Furnaces are supposed to hit the designated temperatures consistently and without a lot of trouble. If the furnace either can’t hit the programmed temperature or shuts off before doing so, it could mean that the entire unit is going bad.
  2. Abnormal noises. Your furnace will make noises from time to time but there are some noises that you should never hear. Thumping, popping, banging, rattling, and scraping noises can all be indicative of a greater problem. Investigate the noises to start and be prepared to call in an HVAC technician.
  3. Yellow burner flame. When your burner is working normally, it will be blue in color. When the flame starts to turn yellow, it could be giving off carbon dioxide. Any other flame than blue could be a sign of a gas leak or an incomplete combustion process.
  4. Frequent repairs. With older or malfunctioning furnaces, repairs will be necessary regularly. If your furnace is in constant need of attention, it could be nearing its end.

Ryan Womeldorf

Ryan Womeldorf has more than a decade of experience writing. He loves to blog about construction, plumbing, and other home topics. Ryan also loves hockey and a lifelong Buffalo sports fan.

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