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Sealed Combustion Furnace: What Makes It Different From a Standard Furnace?


How much do you know about the operation of your furnace? You may understand the basics of how a gas furnace runs: gas burners ignite, hot combustion gas collects inside the heat exchanger, the heat from the exchanger walls transfers to the air, and a blower pushes the air into the ventilation system. But there are some differences between furnace construction that can make a significant difference, such as whether your furnace is a sealed combustion furnace.

If you’ve never heard of the term sealed combustion furnace, we’re glad to explain to you what it is and why it’s different—and often superior—to a standard furnace. If you’re interested in sealed combustion heaters in Fresno as a choice for your home, we can assist you.

Sealed Combustion vs. Atmospheric Combustion

What sets a sealed combustion furnace apart from the “standard” furnace (also known as an atmosphere furnace) is the difference in the design of the combustion chamber and where it draws the air necessary for the gas jets in the burners to ignite and continue burning.

In a standard furnace, the combustion chamber is open to the air surrounding the furnace. If you can look down into your furnace and see the blue light of the flames when the furnace is operating, you have an atmosphere furnace. Because the chamber is exposed to the air, it draws on this oxygen to ignite.

With a sealed combustion furnace, the chamber is completely sealed off from contact with the air in the furnace and the house. Where does it get the air for combustion? It comes through a PVC tube that runs to the outside of the house. The furnace combusts air it draws from the outdoors, rather than from inside the house. 

What Difference Does Sealed Combustion Make?

Sealed combustion is beneficial for several reasons:

  • It’s a more energy efficient method of combusting fuel. An atmosphere furnace will lose some of the heat from its burner flame to the outside, reducing how well the furnace converts fuel into the energy used to heat the air.
  • Sealed combustion prevents the combustion process from creating drier indoor air. If the furnace draws air from the house to work, it causes an air deficit that forces outdoor air to push indoors. Because cold outdoor air is usually dry, it will make the house drier as well.
  • A sealed combustion furnace is generally safer because there’s no chance for flame roll-out where flames escape from the combustion chamber and possibly ignite other parts of the furnace or the areas around it.

Upgrading to a Sealed Combustion Furnace

If you have a furnace that’s 15 years old or more, it’s likely an atmosphere furnace. It’s also time to have it replaced. We recommend that you replace any old atmosphere furnace with a sealed combustion furnace for all the reasons we listed above. If you’re unsure about what to do with your current furnace or if it’s wise to make an upgrade, please reach out to our team and we’ll help you.

Contact Purl’s Sheet Metal & Air Conditioning for all your furnace needs in the Central Valley. Uncompromised Quality & Customer Service Since 1952.

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