What Happens if Furnace Exhaust Is Blocked?

When winter comes around and puts a chill in the air, homeowners all across the country turn to their heating systems for comfort. Most homes generate heat through a gas, oil, or electric furnace. If you have a gas or oil furnace, your home has an exhaust pipe that carries gases from the furnace’s heat exchangers and releases them outside.

You may be wondering, “What happens if my furnace exhaust is blocked?” In this article, we go over blocked furnace vents, what causes them, and how you can tell there’s a blockage. 

At BVS Home Experts, we provide reliable and meticulous furnace installation in Katy, TX, and the surrounding areas. If your furnace is acting up, let one of our knowledgeable technicians inspect and repair it, so you and your family can stay comfortable and safe during the cold season. Call us today to schedule an appointment.

What Happens if My Furnace Exhaust Is Blocked?

So what happens if the furnace exhaust is blocked?

Your furnace uses oil or natural gas mixed with oxygen to create combustion gases to produce heat. The high-temperature combustion gases transfer heat to the air that the blower fan sends through the duct system. The byproduct of this process is combustion exhaust: a liquid vapor composed of carbon dioxide and carbon monoxide that releases through the exhaust flue.

If the furnace exhaust can’t provide proper airflow, there won’t be enough oxygen for complete fuel combustion. Partially combusted gas molecules can pose a health hazard in your home if the furnace exhaust pipe can’t disperse them outside.

When furnace vents have blockages, the gases and fumes produced have nowhere to go. Without clearing the blockage in your exhaust flue, carbon monoxide and other hazardous gases will seep into your home.

How Can I Tell if My Exhaust Flue Has a Blockage?

If your furnace exhaust pipe has a clog or blockage, one or more of the following will occur:

  • Your furnace won’t produce hot air.
  • Your furnace will heat up for a short period and shut down.
  • The front cover panel on your furnace will get hot.
  • Your furnace will emit a strange, unpleasant odor.

Your Furnace Doesn’t Produce Hot Air

The most common sign of a blocked furnace vent is a furnace that won’t heat up. The inducer fan circulates air inside the combustion chamber. There’s a pressure switch connected to the fan that detects whether or not the fan is blowing air.

If the inducer fan isn’t moving any air, the pressure switch will not activate. If the exhaust flue has a blockage, the fan can not receive any air, and the pressure switch won’t click on. The furnace won’t produce heat until the fan triggers the pressure switch.

This safety mechanism prevents the furnace from experiencing incomplete combustion and leaking dangerous gases into your home.

Your Furnace Heats up for a Short period and Shuts Down

Another symptom of a blocked furnace vent is when the furnace kicks on for a short time and clicks off suddenly. Many models of furnaces allow this to repeat for three to five cycles before shutting down completely. This type of short cycling occurs thanks to the flame rollout switch.

If your exhaust pipe has a clog but is letting in some air, the burner flame will come back out of the combustion chamber and into the furnace. When the flame comes out of the combustion chamber, the heat activates the rollout switch, and the furnace shuts down. Once the furnace shuts off, it will start up again and attempt a heat cycle.

If the burner flame keeps triggering the rollout switch, the furnace will fully shut down. Once the furnace enters the full shutdown mode, it won’t turn back on until you reset it. 

The shutdown is another safety mechanism designed to prevent excessive heat from damaging the furnace. It also keeps hazardous gases from leaking into your living space.

The Front Cover Panel on Your Furnace Gets Hot

The air circulating through the system normally pulls the flame produced by the burners into the combustion chamber. The flame will come back out of the combustion chamber into the furnace if the vent has a blockage. 

The rollout switch usually shuts down the furnace when this happens. However, if the rollout switch malfunctions, the flame will heat the furnace’s interior and the front cover panel. If the front panel of your furnace feels hotter than usual when you touch it, the exhaust pipe could have a clog.

Your Furnace Emits a Strange, Unpleasant Odor

A bad aroma coming from your furnace could indicate that something is blocking your exhaust flue. The combustion gases created during the heat exchange process have a distinct odor. When your furnace exhaust vent has a blockage, these gases seep into your home, and the smell can be quite noticeable. 

What Should I Do if My Furnace Vent Has a Blockage?

Furnace vents get blockages from simple things like leaves, dirt, snow, and soot. Sometimes birds and rodents looking for warm shelter find their way into furnace vents only to be asphyxiated by the combustion gases. If you think your exhaust flue has a clog, shut off your furnace and do the following:

  • Clear away any snow blocking the vent by hand. Avoid using a snow blower to prevent damage to the vent.
  • Remove any leaves, soot, or debris from the vent.
  • Check the exhaust pipe for signs of damage.

Call BVS Home Experts

Now that you know what happens if your furnace is blocked, take the right steps to avoid a dangerous situation for you and your family. If your furnace exhibits any of the signs of a blocked exhaust flue, shut it off and call a qualified HVAC technician.

At BVS Home Experts, our staff of trained professionals can inspect your furnace, diagnose any problems, and repair them quickly and efficiently. Whether you need emergency services or a routine furnace check-up, we are here to offer guaranteed comfort and peace of mind. Call our Katy, TX, office today at 281-809-6417 to schedule an appointment.

Author Bio:

Ronald Via

Ronald is one of the key contributors to BVS Home Experts, a family-owned and operated full-service air conditioning and heating company serving the Katy and West Houston areas. With a deep understanding of air conditioning and heating concerns, Ronald brings a wealth of knowledge to our readers.

Table of Contents
    Add a header to begin generating the table of contents
    Fix your Heater or AC
    Free Antimicrobial Treatment
    10% Discount
    AC or Furnace Tune-up
    Sell Us Your AC & Heating System