combustion air and exhaust appear merged

good day americas finest…a mid efficiency furnace with combustion air and exhaust pipes was looking nice and typical to me but theres only one pipe exiting the roof which looked about four inch, and had what looked something like a draft hood, (larger then the bottom pipe so it wasnt simply an adapter) and on top of that a reduced pipe, perhaps 1 1/2 (roof was too steep to walk and I’m getting this via binocs and silly me I didnt take a pic) so when I looked in the attic they were joined by T or something…again couldnt get close but at least got a pic. can these be joined? doesnt that suck exhaust products back as combustion air? only theory I can come up with is there is some kind of pipe within pipe device so theres only one hole in the roof. the ‘draft hood’ looking dealy, maybe a rain deflector for combustion air? well I seek the opinions of those more experienced then I.
mike in MN

That’s what you have.


Yep, and surprised I do not see them more often with cat 4 furnaces.

One hole is easier than two.:wink:

A mid efficiency furnace using a pvc flue…

I doubt it.
Must be a typo.

90% efficiency and greater are condensing furnaces, and require two pipes for intake air and exhaust, and can use PVC due to their lower stack temperatures.

Yes, but keep in mind that many manufacturer’s permit the intake on a 90%+ to be a plastic mesh like cover right at the unit (special part supplied with the equipment) if the space is big enough to provide sufficient “combustion air” (called single pipe venting)

And the exhaust has to be PVC or a special stainless steel (very expensive) due to how corrosive the flue exhaust/condensate is. Typical galvanized single wall or double wall type B/L vent shouldn’t be used on the higher efficiency units because of that.

JMO & 2-Nickels … :wink:

Just a question.
The galvinized pipe to the right. Any perpose in the system?

Mr.C those 2 nickels you keep given = a dime you know.:slight_smile:
Would not the proper use of the phrase be, JMO & a dime?:roll:

thanks for all that input, I greatly benefit. no it was no ‘typo’ when I said mid effeciency…I was just displaying my lack of experience which I exhibit freely in the midst of pros to be able to learn. I thought this to be mid because it had ‘glow plug’ but the burners where right out in the open…i could easily reach right in and burn my little pinkies. I thought high eff was totally enclosed. so again Im open to all input…since I plan to someday be the best darn inspector in the area…have to hurry, 55 old right now so thanks for the help. straighten me out on the mid/high eff

You will do fine.
You attitude is commendable. The ability to see ones errors is most important.
I made and still make errors. We are all human.
Great question. Keep asking.

It’s a US thing, eh … :stuck_out_tongue: … and sometimes it’s a quarter due to inflation … :wink:

And you will get there if you keep asking good questions about things you dont understand or haven’t seen before … :wink:

Typically the combustion chamber on a 90%+ high efficiency furnace would be enclosed. What was the make and model for the furnace?

If you have some time, take the advanced HVAC course offered here. I just finished it and learned alot about the different units.

Thanks for reminding me to finish my advanced course.
Mr. Mele or (Mr.Apple)and Kenton as the streight man do a great job of explaning the HVAC system in detail.
Be prepared for a 4 or 5 part course last time I looked.
Bring you note pad with you.Loads of detialed education.
Take your books young man and sit in the front where I can watch you better.:roll: who me!!
sorry teacher.sorry class.

Gotta say it is a long course and I did find my eyelids getting a litle heavy. I would watch for awile and then take a break. The last video has some guy (Ben) ripping apart a furnace to find a cracked heat exchanger which I found pretty funny. :mrgreen::mrgreen::roll::shock:

info on the concentric vent termination kit was highly beneficial since I have no doubt I will encounter that again. My new dilemma brought on by you guys is the ‘what furnace is this’ question with open burners and pvc venting. I recorded that in the report and had a ‘oh crap I did that?’ moment when I forgot to take my copies of the report. have arranged to obtain them at which time I will start a new thread on this to make sure and get it straightened out in my mind. thanks for the great help…glad you guys arent my competition.
mike in MN

Greg I will send Ben some of my tools so he does not cut his hands to pieces.
If his hands get infected and Nick shakes his brothers hand, he may very well to fall ill to some strange disease…
Then leaving all INACHI members leaderless.

After several months it will all start unraveling.
After a half a year you will see INACHI inspectors roaming the streets on the hands and knees say " Nick, Nick what happened"
“you should have taken better care of your brother.”
All mumbling and foaming of the mouth.
Then civil unrest, just at the onset and preciser to the biblical revelations.
Gees Louse I better mail him my tools now to save INACHI.:roll:

PS: His wife gave him an ear-full last time he took the homes furnace apart to shoot a INACHI educational video.
I wonder which of the 2 scenario’s is worse. HA HA HA.

Any furnace with plastic (CPVC or ABS ) is high effiency.

Mid efficiency furnaces use a “B” vent (metal)


Ahhh … it is possible (but not likely) that someone didn’t know what they were doing venting mid/standard efficiency equipment, and cousin Bob had plastic venting which is sooooo much easier to install … so Harry Homeowner takes a trip to home cheapo …

Always try to take photos on an inspection to document conditions even if you don’t include them in a report. It can get your butt out of a pickle if say there are belongings, throw rugs, furniture, etc. that cover a problem which become obvious when the owners move out. You get the call weeks/months later … “how come you missed this huge problem thats going to cost me a lot to fix … you have insurance, right?”

Also take some shots of all equipment labels, in case you forget to write that down or there is a discrepancy and you cant decode what you wrote down … :idea:

JMO & Quarter … :wink: