We need to replace our 20 yr old furnace, and were considering getting a 90+
efficiency furnace. But then they'd have to vent it out of the wall, and we
have a big deck above where it would come out of the wall. Code requires
that the venting cannot end under a deck, so the options are to put a hole
in the deck and run it above the deck (which wouldn't look that great when
we're on the deck), or to run it under the deck and extend it about 12 ft
under the deck, so it vents at the end of the deck.
Problem is we live in Minnesota, so the venting in this last method would
have to be heavily insulated.
Some contractors say this running the venting under the deck for 12 feet
with insulation would be no problem, they do it all the time, it never
freezes and they say it's listed as an acceptable method in their
installation manuals (i.e., for a Carrier furnace), it meets code, and they
don't have problems when its done properly.
Other contractors say to never do that because the piping would surely
freeze when that much of it is in the open, leading to all kinds of
Which contractors should we believe? Is the under the deck method OK to do,
or would it freeze? If we did the venting above the deck, is there an easy
way to make it so it doesn't look so out of place and so we don't bump into
it and risk the piping breaking (especially in cold weather)?