I notice smoke from my neighbor's furnace vent (outside one which is in the roof) in the early AM or night when their furnace/heat is ON. Same thing does not happen for my outside vent when my heater is on. This happens all the time irrespective if it is very cold outside or not. Note that I live in a community where all houses have a gas based furnace.
Can anyone advise if I should be concerned? I am also not sure what this smoke is. So please educate me if possible.
Thanks in advance.