The question was asked:
"And is part of the burn product an acidic?"

I think part of the problem with idealized solutions is that they
sometimes don't take into account seemingly unimportant real-world
effects.  For instance, city gas that's plumbed to homes isn't even a
constant mix.  These differences are so great that regulated utility
companies adjust their price per cubic foot to hold the $ per heat
value unit constant.  The presence or absence of impurities which when
heated in the combustion process produce nasty stuff like sulfuric
acid, is tiny in terms of their quantity, but important in their
effects if you let it condense on your metal equipment.  It can eat a
non-stainless steel heat exchanger through in a single heating season!

I think that if the propane we buy didn't have any other molecules
hiding with it, we wouldn't have any acidic combustion byproducts
other than carbonic acid, which we usually call carbonated water.
That's the same mild acid plant roots use to eat through some rocks
like limestone.  Give it time and it will eat.  But I just buy the
stuff they sell at the propane vendors.  If anyone wants to catch a
few ml. of propane combustion flue gas precipitate and test its ph.,
please post your findings.  Until we have that kind of information, I
suggest it's prudent to error on the side of caution.
John