Venting new condensing furnace below a deck?

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 problems.
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)?
--
DK



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Even vented correctly, you will inadvertently have a pipe freeze, especially longer runs in unconditioned areas. Proper venting is however the best deterrent to have the least problems. Vent it out to the end of the deck and see how well it works. If it freezes then cut the pipe back and vent it up through the deck. Paint the PVC to blend in with the wall or deck color. Whatever you do or have done FOLLOW the manufactures installation instructions for proper venting. Bubba
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Can you go up the chimney with the PVC?

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Have them give you references you can contact where they did this 2 years ago so you can see if they have had any problems with it.

ask the contractors give you other options
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There would be no problem running it under a deck, even in Minnesota hehe. You may need to use larger pipe 3" rather then 2" if the run is too long, but as long as you use armaflex, or some type of insulation you'll be fine. Keep the snow clear from the termination, and make sure the venting is sloped properly. Where I'm from you can only vent under a deck, if it's open on 3 sides (lattice counts as open), and you have a foot from the bottom of the deck and a foot from grade. Hire a good installer to put it in. Don't be afraid to read the manual and double check the termination is correct and all looks well. You'd be suprised how many "pros" can mess it up.
And on the topic of venting, I just read an article that sais they will be banning the use of ABS for venting a high efficiency furnace.
-Canadian Heat
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believe the contractor who puts it in writing with a guarantee to fix it if it fails to perform to specifications.

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