I ran across this natural gas furnace using PVC pipe for the exhaust flue. Is that OK? I don’t normally see PVC being used for a flue. Thanks.
It’s a high efficiency furnace.
There should be one for combustion air as well… Looks like it is missing??
And don’t let the contractor tell you it is ok, it should be drawing combustion air from outside.
Are you a practicing home inspector?
There is a vent in the floor. It’s drawing combustion air from the crawlspace.
Not all High Efficiency furnaces draw there combustion/dilution air from the exterior. While you often see two pipes, it is not “always” the case.
Only when the contractor wants to save 30 feet of pipe. 
High efficient furnaces are sealed combustion units, they don’t draw from a vent. They draw from another pipe that should be beside the exhaust pipe, and run outside. Right now that furnace is drawing air from the room.
http://i.treehugger.com/files/th_images/high%20eficiency%20gas%20furnace.jpg
From Goodmans Install Manual"
Dual certification means that the combustion air inlet pipe is optional
and the furnace can be vented as a:
Non-direct vent (single pipe) central forced air furnace in
which combustion air is taken from the installation area
or from air ducted from the outside or,
Direct vent (dual pipe) central forced air furnace in which
all combustion air supplied directly to the furnace burners
through a special air intake system outlined in these
instructions.
I still don’t like it, I always recommend they be installed to the exterior of the home.
Atta Boy Donald good post.
Personal choice should not enter into a home inspection its either right or its wrong no gray areas. An inspector could end of paying for the pipe if not careful???
True, but I don’t carry an installation manual for each manufacture around with me. So, IMHO it should be pulling from the exterior. To me it is just a workmanship thing.
Some of the ones that I have seen that are allowed to draw air from the interior do not even have a place to install an intake pipe.
I too am big on workmanship but If I wrote up everything just because I would not have done the work that way I would be a very busy person.
I personally don’t like flex duct but its not up to me to say (don’t use it) or its wrong???
Me too:)
Here’s one. It’s an Amama.
This is the problem with that scenario:
Choose a sealed-combustion furnace that uses 100% outside air for combustion. Indoor air contains traces of commonly used household products such as bleach, paint strippers, and so on. Condensing furnaces have been known to corrode rapidly if fed indoor air contaminated by these common products. Most manufacturers void warranty coverage for furnaces operated in a contaminated atmosphere. Even fabric softener and salt from water softeners have been suspected culprits. Unless the furnace is near a possible source of contaminants, such as a dry cleaning shop, outdoor combustion air is much better for the furnace.
See post, above. I wouldn’t recommend that scenario, that’s all.