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BillyHvac, Journeyman HVAC Tech
Category: HVAC
Satisfied Customers: 22006
Experience:  Endorsed for unlimited heating, cooling, oil burners, boilers, refrigeration, hydronics
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Cracked Firebox My oil forced-air furnace has developed a

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Cracked Firebox
My oil forced-air furnace has developed a crack between a couple slots in the ceramic material the flame is contained in. Thay tell us that if the crack widens and box collapses, we will get soot circulated into the living space.

Since the heat exchanges separates the combustion products from the living-space air, that the soot would not be an issue - that is, until the heat exchanger burns through from being hit by the flame. Am I correct?

The furnace is being replaced this week, but I am curious.
You are correct. The flame will impinge and soot the inside of the furnace, but will not soot the home until it is sooted shut an cannot draft. Then it puff out the front of the burner gun, damper or inspection port.
Customer: replied 6 years ago.

Ok, so the issue is that the flame will not burn clean, and so produce more soot than usual? Then when the flue is sooted shut, you get the "puff" - right?


So, I will have a mess by the furnace in the basement, but not throughout the house, right?


I would think that it would take a couple days or more to build up that much soot, so if I check the firebox daily, I can leave the furnace running until it is replaced - right?

Yes you are right. The mess, if any, will be at the furnace. as long as the ceramic pot does not fall directly into the flame pattern you will not have an issue. And even if it did it would take a while to soot the unit shut.
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