What Causes a Puff Back and How to Deal With It?

We’re writing this shortly after Christmas Eve 2023 and New Year’s Eve 2024. The holiday season is already here, and for many of us, that also means colder weather and possibly even freezing temperatures.

Winter, however, is often the time a lot of homeowners deal with unexpected issues in their properties that lead to some kind of damage. 

For instance, winter is when pipes often freeze and burst, families indulge in endless cooking which sparks fires, and when our heating systems release something called a puff back.

It’s the last one we’ll discuss today – what is a puff back, what causes puff backs, and what to do when they happen. 

Let’s dive right in!

What is a Puff Back?

A puff back refers to a sudden release of smoke or soot from a heating appliance, usually a furnace or a boiler. 

It happens when there is a buildup of unburned oil or gas vapors in the combustion chamber, which then ignites in a small explosion. This explosion can force smoke, soot, and other debris back into the heating system and, in a lot of cases, further into your rooms.

Puff backs can damage the heating system and create a lot of mess in the affected areas of your house. They are often characterized by a loud “puffing” sound, followed by the release of smoke or soot, hence the name. 

They may happen due to various reasons, including improper maintenance, a malfunctioning ignition system, or a blocked flue. This brings us to…

What Causes Puff Backs?

Some common causes of puff backs include:

  • Incomplete Combustion: When the combustion process in a furnace or boiler is incomplete, unburned fuel vapors can accumulate in the combustion chamber. The ignition of these vapors can result in a puff back. Incomplete combustion can also result in the release of carbon monoxide, a colorless and odorless gas that can be dangerous in high concentrations.
  • Blocked Burner: The burner in a heating system should be clean and free of any obstructions. If there is a blockage, it can disrupt the proper flow of fuel and air, leading to the incomplete combustion we’ve mentioned above.
  • Ignition Issues: Malfunctions in the ignition system, such as delayed ignition or ignition failure, can contribute to the accumulation of unburned fuel vapors. Then, when ignition finally occurs, it may lead to a sudden release of energy, which causes puff backs.
  • Dirty or Clogged Heat Exchanger: A dirty or clogged heat exchanger can hinder the efficient transfer of heat. This can lead to the buildup of unburned fuel.
  • Excessive Oil or Gas Accumulation: Over time, oil or gas may accumulate in the combustion chamber, especially if there are leaks or problems with the fuel supply system. 
  • Improper Venting: Blocked venting systems, like a chimney, can contribute to the buildup of combustion byproducts, including unburned fuel vapors.

Are Puff Backs Dangerous?

Depending on how much gas has accumulated, puff backs can cause more or less damage.

The subsequent soot and smoke from puff backs can be hazardous if inhaled, particularly for individuals with respiratory conditions. The fine particles in soot can irritate the lungs and worsen existing respiratory problems.

That soot will also damage your nearby walls and furniture, which can be difficult and costly to cleanup. Removing soot on your own is dangerous task and it should often be left to professionals. Puff backs can also damage your heating system.

The explosion can sometimes cause fires themselves. Even if the explosion itself is small, it has the potential to ignite nearby flammable items.

How to Prevent Puff Backs?

First and foremost, schedule an annual professional inspection of your heating system. 

A qualified technician can thoroughly clean and inspect the furnace or boiler, checking for any signs of wear, blockages, or malfunctioning components. 

Do this before winter, when you’ll use your furnace or boiler the most.

Additionally, pay attention to any unusual sounds or oil odors coming from your heating system. In such cases, shut down the heating system immediately and contact a professional to see what’s going on.

Regularly inspect, clean, and replace air filters to ensure proper airflow. How often you do this will depend on the type of filter. For instance, fiberglass filters will need to be replaced more often (between 1 and 2 months) than HEPA filters (up to 3 months).

Be mindful of any changes in fuel consumption or heating efficiency. Sudden spikes in oil or gas usage may indicate a problem with combustion.

Maintain a clean and unobstructed flue or chimney. Regularly check for debris or blockages and ensure proper ventilation.

What to Do When a Puff Back Happens?

As we’ve said before, as soon as a puff back happens, shut off your heating system by locating the emergency shut-off switch or turning off the power. Open up your windows and doors to ventilate the space and call a professional to take a look at your furnace or boiler.

If there’s a strong odor, evacuate the room and call a gas company for assistance. In case of a fire, call the fire department.

The heating repair technicians will take care of the appliance itself for you, but the leftover soot or smoke will need to be cleaned up by a fire restoration company.

Again, it’s recommended that you refrain from cleaning these up on your own. You likely don’t have the know-how and equipment required to do this safely and thoroughly.

Puff backs are typically covered by insurance, depending on the cause. In this case, you’ll not pay for fire restoration. The caveat is that the insurance may not cover the repairs or replacement of the broken-down appliance itself. Look into your policy and learn more about fire damage insurance.


Thank you for checking out today’s post on puff backs. Hopefully, you now know what causes puff backs and how to properly deal with them.

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