HE Gas Furnace Exhaust/Intake

Looking for the science behind what I saw last night. I inspected a Heil high efficiency gas furnace that had the exhaust exit one side of the building and the intake on a completely different side of the building. I was always under the impression that the exhaust and intake pvc should exit the building within 12-24" of each other. I looked up the manufacturer’s recommended install and it stated within 12" so I will document it as improper install but I would also like to understand the science. Can someone tell me why or point me in the direction of why the exhaust/intake needs to be in close proximity to each other (pressure zone?) and then what would be the possible effects of the set up that I explained. I appreciate any insight…thanks!

Me thinks your reading it wrong should not be closer than 12 inches as some dummy would try to install them within 6 inches of each other. I know of nothing stating they can not be 3 feet 10 feet or 25 feet from each other one is discharge and one is intake simple as that

Here’s the link to what I was reading, Charley:


Page 5 shows the upflow diagram that states “terminations in the same atmospheric zone”. Also, on page 11 and point number #14 it restates this. Am I misunderstanding that?? I guess I’m not certain what the same atmospheric zone means??

The same atmospheric zone means both to the outside. Doesn’t mean can be on opposite sides of the building. The only thing I can think of that would affect it is if one is windward and one is leeward. But looking at the docs, they can’t be over 20’ apart. Just my 2 cents.

Thanks for the responses, guys!
I appreciate it!

It is about differential friction loss, if the pipes are not the same length, and number of fittings (fitting equivalent length).

The fan is an inducer fan, not a pump.

Good stuff, David!
I had to look up differential friction loss and found some good info ( and a whole lot of equations:shock:) that gave me an even better understanding.