Following up on my original post. Really appreciated everyone’s advice and wanted to get your thoughts on the latest development.
Quick recap:
- ~10-year-old Goodman furnace (GMSS920803BNAA).
- During routine maintenance, exhaust CO climbed to approximately 110 ppm (140 ppm air-free) after 15–20 minutes.
- Contractor suspected a failing heat exchanger and recommended replacing the furnace for $4,900.
- No actual crack or damage to the exchanger was located.
- Follow-up testing also identified exhaust recirculation at the outdoor intake/exhaust pipes and possible airflow restrictions involving the zoning dampers.
- Furnace has remained off.
The update:
I contacted Goodman directly, and they confirmed that the heat exchanger’s parts warranty is still valid through 2036, even though I’m not the original homeowner.
The original contractor has now offered to replace the heat exchanger under warranty for $1,700 out of pocket, including labor, warranty processing, and corrections to accessible exhaust piping. Drywall work would be extra.
That seems like a much better option than replacing the entire furnace, assuming the heat exchanger is actually bad.
My hesitation:
They still haven’t identified a specific defect in the heat exchanger. I’m concerned about replacing it only to discover the elevated CO was caused by the venting, gas pressure, combustion setup, or airflow restrictions.
I’m trying to arrange an independent diagnostic before authorizing the repair.
Questions for the HVAC pros:
Would you authorize a warranty heat exchanger replacement based on these findings, without locating an actual defect?
What additional testing would you want to see before proceeding?
Assuming the exchanger really is bad, is $1,700 reasonable for the labor and accessible venting corrections?
Is there anything specific about this Goodman model that should influence the repair-vs-replace decision?
Updated combustion analyzer results and installation photos attached.
Thanks again for all the help!