A homeowner's account of finding a large, irregular tear in a furnace exhaust connector eight days after a cleaning service led to urgent concern about carbon monoxide exposure.

Here's what to know

The homeowner sought advice in a Reddit post on Nov. 4 and shut off the furnace. The damaged section was hidden behind a bend above a garage water heater, as they revealed in a picture posted to the r/HVACAdvice subreddit.

A shared roof exhaust appeared to serve both the Rheem water heater and the natural-draft Tempstar furnace, which was built in 2000.

The garage's gassy smell had cleared by the time the damage was discovered. The homeowner first noticed the odor on Oct. 28, following an Oct. 27 service visit that cost $360 for duct cleaning and $150 for furnace/blower cleaning.

A user reacted with alarm: "That is your exhaust!!! Do not run the furnace until that has been replaced, you're just dumping exhaust gases and carbon monoxide into your house. Did they do any work close to this vent?"

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More background

The record of a utility's Sept. 30 carbon monoxide check contained no vent inspection. Its readings were approximately 180 parts per million in the flue, with none detected at the supply vents.

No tear was noted in the flue pipe check from a contractor's Oct. 15 diagnostic, which reportedly recorded carbon monoxide at zero ppm. The heat exchangers reportedly showed rust or oxidation, but no cracks were noted.

Age-related deterioration was one possible explanation the homeowner raised. Damage from handling during the cleaning was another. A pleated MERV 8 filter replaced one the homeowner described as heavily loaded. They also reported persistent indoor dust.

What can be done?

"Thanks for replying and yes I have turned off the furnace now! And yes along with duct cleaning, they also cleaned the furnace as well," the original poster confirmed.

Commenters recommended replacement rather than an attempted repair with tape. 

"Flexible exhaust should not be legal," one poster declared. "Replace it. Nightmare fuel in my book."

The homeowner said DuraVent's instructions likewise called for damaged parts to be replaced immediately, which backed up the community's consensus.

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Where can I learn more?

A torn furnace vent is just one heating problem that can raise carbon monoxide concerns. 

• A homeowner discovered a loose furnace flue after AC work and received warnings against running it.

• A homeowner's rusted-through flue pipe prompted technicians to warn about potential carbon monoxide exposure.

• A Philadelphia homeowner received a $4,900 furnace quote after carbon monoxide testing; technicians urged further checks.

• A Texas inspector discovered a new-build vent flaw that could spill carbon monoxide into the attic.

• An inspector flagged carbon monoxide risk around an old Utica boiler; the seller's HVAC technicians tested gas lines.

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