My last gas furnace was installed over twenty years ago and vented directly outside. I don’t remember that running twenty feet of three inch plastic pipe cost all that much.
The problem comes when you have a rear level walkout with a finished basement. You would have to rip out your ceilings to run the pipe to the back or side of your house. The alternative is to have a constantly hissing pipe sticking out the front of your house right next to the front door. That’s my situation. I looked at getting one of the energy efficient furnaces about five years ago and decided against it immediately.
I'll admit, that part of the article made me scratch my head. I've never seen a gas furnace vented through a chimney - all of mine had separate vent stacks. Maybe this reference is an upper east coast sort of thing dealing with older houses.
You're forgetting one important fact!
First of all, you need two pipes, a combustion inlet and an outlet vent. And they must be separated by at least four feet. Code also calls for a 6 inch diameter insulated outside connection to the cold air side of the furnace air and also an automatic damper on it. You must also deal with the acidic condensate. If you don't have a drain near the furnace, you may need a condensate reservor and pump. Then you also need some place to pump it.
“I dont remember that running twenty feet of three inch plastic pipe cost all that much.”
We remodeled 15 years ago and put in a flue for a new furnace which we had removed when we re-roofed a year ago because we put in a 92% efficiency furnace which used 3 inch plastic for both the combustion air intake as well as the exhaust. Knock on wood, the thing has worked great. It’s so efficient that it has a “condensate pump” that pumps the water from the combustion process into the sewer.