Old house odor in a condo
If you can not find the source of the odor or want a temporary/permanent fix try using a charcoal filter in the cold air return of the furnace. I use a filter from Home Depot or Lowes called a "web absorber" model#FPR-5 at about $12.00. It is a 20"X25" cut to size filter that I used to replace the pre-filter in my electronic air cleaner. My wife is like you in that she can smell a "flies fart" at 10 miles. I have been using them for about 15 years and she is happy and so am I .