Not sure, but believe at least a heating season. The vinyl is more melted than it looks in the pic. I think what is keeping it from excessive heat is that the flue products don't actually vent - as you can see by the furnace, there is a lot of spillage. Good that they are living in essentially a screened in porch when it comes to building tightness.
now thats freakin dangerous and stupid,,,just heat wont hurt nothin yeah right.these people did not have a conscious the vent /pipe would melt and could kill everyone .dont stuff like that just burn my patience.
Large 2-story inner city house whose occupants felt they could not afford to have a pro look at it. Homeowner repair. Obviously did not know what they were doing. Was wrong about length of time it had been like this. Just this heating season.