"Ray" wrote in message
news:SGAXd.32041$QQ3.19993@trnddc02...
I live in an old six-unit apartment building which is heated by oil-burning
furnace.

For most of the time on cold days, we can see a fair amount of steam
coming out of the chimney.

Obviously some heat is being lost. The question is whether this is normal.
I don't recall seeing this steam coming out of other older buldings in our
area.


Yes, it is natural. Most oil burners are about 80% efficient and the rest
of the heat is going up the stack. Fuel also contains some moisture, as
does the air for combustion. This goes up as vapor and will condense and be
visible as it eaves the stack in the cold air. You don't see it all the
time as conditions vary.

If you are seeing black smoke, the burner is in need of cleaning and/or
adjusting. That is very wasteful as it is fuel that is not completely
burned and thus wasted.