…when he came and worked on the furnace.
That would explain it. He got the HE furnace in, but forgot to:
A. Re-install the water heater flue.(It was laying in pieces)
B. Close up the gaping holes in the return vent 5 feet away.
C. Have a license to do any of the work.
To top it off the 70 year old lady living alone in the house didn’t have a working CO detector and all the furnace work happened 3 years ago.