Thread: Heat exchanger at draft hood

in this 1978 FlameMaster gas-fired forced air furnace, some packing is missing in the joints where the top ends of the heat exchanger pipes meet the draft hood, leaving little gaps. Is this serious? The furnace is otherwise in good condition for its age and has been regularly serviced.

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Originally Posted by Frank Norman

in this 1978 FlameMaster gas-fired forced air furnace, some packing is missing in the joints where the top ends of the heat exchanger pipes meet the draft hood, leaving little gaps. Is this serious? The furnace is otherwise in good condition for its age and has been regularly serviced.

I don't think I would even begin to say it is in good condition! Even though it might look like it is in good condition, a 33 year old gas furnace is about 20 years past it's expected life.

It is hard to tell but the last chamber looks like it might be leaking flue gases up in the draft hood, out onto the side of the cabinet.

I would only report that the furnace is well past it's expected life and that future operation should be considered good fortune!

[quote=Scott Patterson;158561]
It is hard to tell but the last chamber looks like it might be leaking flue gases up in the draft hood, out onto the side of the cabinet.


Scott may have part of this right, but flue gases go into the draft hood anyway. The fact that some flue gases may be directly impinging on the side of the draft hood is not correct. See the rust pattern. What could ALSO be getting into the draft hood is excess CIRCULATING AIR from the gaps around the openings of the heat exchanger where they enter the draft hood. Excess air in the draft hood and vent is NOT a good thing. This can lead to rapid cooling of the exhaust gases and condensation in the vent or draft hood. It may also affect the draft.

I suggest testing this theory by allowing the draft hood and heat exchanger to cool to room temp., then turn on the furnace blower. You should NOT feel air flowing out of the furnace into the draft hood. If you do then recommend correction by a qualified HVAC firm. If you elect NOT to do the test, then call for further evaluation - correction by the qualified HVAC firm. I agree that given the conditions shown, the furnace is at the end of its service life and would recommend evaluation - correction by a qualified HVAC firm.

Given the proximity of the tube to the side of the furnace you would expect to see some signs of heat after 33 years. With naturally drafted furnaces like these, the flue gasses tumble a bit on the ends because the flue is centered. A smoke test would determine whether the heat exchanger has any problems, but this furnace has gone above and beyond it's expectations and should be replaced with a more efficient unit.