I need to replace the inducer in my ICP furnace model NTC6100GFA1. It is still working, but it has both a rattle and a high-pitched bearing whine that I'm sick of hearing.

My only questions regard the connection between the inducer assembly and the exhaust flue, shown in the picture.

In every video I've seen online that shows replacing an inducer, they easily disconnect and obviously had only a friction fit. But mine is so immobile that I think it must have been sealed together -- I'm guessing with RTV or something similar. I tried removing the sheet metal screws in the long vertical duct part above and it will not budge either, even wiggling and twisting with the inducer unscrewed from the furnace. (The old inducer was installed about 15 years ago.)

Does that mean I will have to cut off the flue duct and replace that part of it? Or is there a simpler trick I'm just missing? (I live in Illinois, US in case there's a Code requirement here that might be relevant.)

Thanks in advance! enter image description here

UPDATE: After the replies and suggestions by Ecnerwal and Isherwood both of whom assumed there'd be no adhesive, I tried this again, applying more tapping and stronger force. I found that all torque applied to the duct gets transferred through to the inducer housing itself, trying to loosen it from the furnace screws instead of what I need to happen. I also tried prying a bit at the joints which accidentally bent some of the duct outward. It looks like RTV red or similar underneath, so this blasted thing is solidly glued on. See close-up pictures I've just added. So it seems I will have to cut off this flange and replace the connection (with a band clamped joint instead, on the inducer end)


  • There's no sign of sealant there. Is the pipe above actually free to move up, or is it restrained beyond the picture preventing it from moving?
    – Ecnerwal
    Commented Dec 7, 2023 at 16:26
  • I tried removing the sheet metal screws at bottom (shown) and top ends of the long straight pipe above it, and knocking loose as much corrosion particles as I could and still none of those 3 joints would budge at all.
    – ybull
    Commented Dec 7, 2023 at 16:29
  • 1
    Smack it from side to side (with the screws out) using something like a sandbag or beanbag against the pipe so you don't dent the pipe when smacking it. I'd leave the inducer screwed in until the pipe breaks free.
    – Ecnerwal
    Commented Dec 7, 2023 at 16:33
  • Before you abandon all hope and start cutting metal, have you tried slicing through the joint with a razor blade? If it's some sort of RTV or (more likely if this was done professionally) a squeeze/brush-on duct sealant, it might just cut cleanly off.
    – FreeMan
    Commented Dec 7, 2023 at 19:10
  • Take all the screws out and then bang on it.
    – Mazura
    Commented Jan 7 at 12:43

2 Answers 2


Unless there are sheet metal screws from the outside it's probably just stuck. Corrosion from dissimilar metals may have bonded them together. Or maybe oil from the manufacturing process hardened.

At any rate, use a combination of light impacts, wiggling, heat, and force to break it free.

  • I already tried all those things. Except applying heat. But I can't imagine that helping, since it's had 15 years of furnace exhaust going through it. :)
    – ybull
    Commented Dec 7, 2023 at 16:30
  • 1
    Imagine harder. Heat expands metal, so if you just heat the duct it may loosen things.
    – isherwood
    Commented Dec 7, 2023 at 16:41

Shift your focus upward -- starting at the furnace there's a reducer sitting on the 3" furnace outlet, then a section of 4" flue sitting on top of that reducer. What's next, above the view of the photos here? Most often there's an elbow fitting within 3-4 feet above the furnace.

I'd separate the vertical flue section from the elbow or separate the elbow from whatever pipe comes after it. If you can separate the flue at that elbow you'll have a few feet of vertical flue that can be used as a lever to wiggle the reducer fitting off the inducer outlet.

  • I already tried that even before posting the question, and yet again later. That joint is also apparently sealed. And as I said in the update, all leverage applied to the duct ends up transferring beyond the joints I'd like to separate, and instead tries to loosen the long screws that attach the inducer to the furnace.
    – ybull
    Commented Dec 9, 2023 at 19:14
  • 2
    @ybull Since you're planning to replace the inducer anyway, if the reducer piece won't separate even when a few feet of pipe are used as a lever, grab the tin snips or recip saw and cut off the wide part of the reducer fitting. Don't worry about separating it from the old inducer housing. A new reducer, few feet of pipe, and handful of screws are going to cost under US$20. I like to disassemble neatly too but sometimes it just makes more sense in time and dollars to cut & replace a stubborn part that's blocking progress.
    – Greg Hill
    Commented Dec 11, 2023 at 0:23
  • Greg, yes, that is what I had to do. I had it in mind as the last resort before even posting this question. The original bolded part "Does that mean I will have to cut off..." And yes, the cost of parts was fairly minimal.
    – ybull
    Commented Jan 11 at 20:42

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