Furnace Heat Exchanger: Temporary Repair

Which small spot on this hot-air furnace heat exchanger isn’t like all the other small spots?

Pinhole in furnace heat exchanger
Pinhole in furnace heat exchanger

Correct! The orange one at the corner of the rectangular exhaust gas flue that’s lit up like the sun, because you’re looking directly into the oil burner flame.

With the fire off and everything cooled down, it looked like this:

Pinhole in furnace heat exchanger - detail
Pinhole in furnace heat exchanger – detail

Now, this calls for a new furnace (because replacing the heat exchanger costs as much as a new furnace), but as it turns out this was in an unoccupied house during the week before Christmas. So I scrubbed off the debris with a steel brush, bent up a snippet of 2 mil brass shimstock to fit the corner, applied a layer of JB Industro-Weld epoxy to the problem, and positioned 200 W of incandescent bulbs to help it cure slightly sooner than forever:

Furnace heat exchanger - temporary fix
Furnace heat exchanger – temporary fix

That is most certainly not a final repair, not just because the heat exchanger’s normal operating temperature exceeds the epoxy’s 500 °F rating, but because where there’s one pinhole there’s bound to be more. The goal was to let us keep the furnace running until we could schedule the replacement after the holidays. Remember, the building isn’t occupied and neither of the smoke / CO detectors went off at any point in the proceedings.

Houses are trouble!

5 thoughts on “Furnace Heat Exchanger: Temporary Repair

  1. This “temporary” repair might end up lasting longer than you expect. I think it would be simpler to just list the things that JB Weld can’t fix. :-) My only caveat is the observation that if the stuff is thick enough to work with, it’s too cold to set (and vice versa).

    1. It does come in handy for a remarkable number of jobs around here…

      There’s a slobber of epoxy just forward of the brass shim in the “after” picture: the stuff did get runny in the heat. That hole seems well plugged, but any others where we can’t see them will just remain as they were.

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