not on your older furnace. it doesn't burn clean enough. and it
routinely requires a hot exhaust updraft discharge up a chimney to
specified feet above the rooftop.
you're probably looking at a 99 percent efficient combustion of gas on
those pvc ground level flues.
i searched google for "high efficiency oil heat pvc flue"
and came across a good article about how much maintenance they save
with a change:
http://www.hammerzone.com/archives/h...ermination.htm