Why Does My Furnace Smell Like Gas When Turned On? A Kansas City Tech Explains
November 01, 2018
Natural gas is dangerous to inhale, and it’s also highly flammable, which means if your smelling it you’ll want to take safety precautions immediately.
We’ll walk you through what to do.
First of all, let’s determine where you notice the smell:
- Do you notice a faint gas smell near your furnace (the indoor unit) when it’s turned on? You probably don’t need to worry. It’s normal for your gas furnace to occasionally emit small amounts of gas when it’s cycling on. But if you notice this faint smell persistently, or it gets stronger, you may need a furnace repair.
- Do you notice a strong, rotten egg smell odor coming from your air vents when you turn on your furnace? If so, it may mean your furnace has a gas leak, which is dangerous for you and your family.
In this article we’ll explain…
- What to do if you smell gas coming from your furnace
- What causes gas to leak from your furnace
What to do if you smell gas coming from your furnace
If you’re smelling a strong gas odor from your furnace or air vents, follow these steps:
- Turn the furnace off via the thermostat.
- Open windows to ventilate the gas.
- Turn off the gas main to shut off the gas supply to your furnace. You can watch this helpful video for more information about how to shut off your gas main.
- Stay out of the house so you don’t breathe in the gas fumes.
- Call your gas company to inspect your home and make sure the problem is with your furnace and not the main gas line or gas appliances like a stove, fireplace or water heater.
- Contact a furnace professional to diagnose and repair any furnace problems.
What causes gas to leak from your furnace
If you smell a strong gas odor when your furnace is running, it’s likely because of these 3 issues:
- A cracked heat exchanger
- A backdrafting furnace
- A gas line or valve leak
Let’s go into more detail about each of these causes.
Cause #1: A cracked heat exchanger
Your furnace’s heat exchanger is the component that actually heats your home’s air. Here’s how your heat exchanger is involved in the heating process:
- Gas combusts then enters the heat exchanger.
- Cold air gets blown over the exterior of the heat exchanger, which heats the air.
- The heated air enters your home via the ductwork and registers (vents).
Several things can cause a heat exchanger to crack, but the most common issue is overheating. When a heat exchanger cracks, combustion gases (including natural gas and carbon monoxide) can mix with the heated air and enter your home’s airstream.
Since a cracked heat exchanger is a safety risk to your family, you’ll want to get it fixed ASAP. Unfortunately, a cracked heat exchanger is an expensive problem—often it’s more cost-effective to replace your entire furnace than to replace your heat exchanger.
Learn more about replacing your heat exchanger by reading our article, “Should You Replace Your Heat Exchanger or Get a New Furnace?”
Cause #2: A backdrafting furnace
Backdrafting is when combustion gases from your furnace leak into the surrounding area (or even your home’s air) instead of exiting your home safely via the exhaust flue.
The most common causes of a backdrafting furnace are:
- Disconnected, leaky or clogged flue
- Running too many exhaust fans in an airtight house
- Leaky ducts
You’ll need to have a furnace repair pro inspect your furnace and fix any issues that may be causing backdrafting.
Cause #3: A gas line or valve leak
Natural gas is delivered to your furnace via gas lines. The gas valve controls the flow of gas entering into your furnace from these lines.
If either one of those components have a leak, you’ll definitely notice a strong gas smell.
Common reasons a gas line or valve could be leaking include:
- Age (leaks due to general wear and tear)
- Improper installation
- Accidental damage
Again, you’ll need a furnace professional to fix your gas lines or gas valve if they are leaking.