Inspecting High efficiency furnaces

What are the top two repairable type items found by you while inspecting high efficiency furnaces.


Almost all involve poor exhaust placement or lack of proper allowance for makeup air Charlie.

I am making a list and checking it twice yours is noted:D

Poor slope of exhaust to allow condensation to flow back to the distilate drain.

and believe it or not poor glueing or lack of glue to the intake and exhaust lines!

noted: I will post my top two after the list grows a bit so far no one has ID mine for my area

Combustion air intake piping missing/not going to the outside.
Dirty air filter.

Condensate leakage into interior of furnace cabinet.

Venting: ABS glued to PVC.


Noted your # 1 is my # 2:D

Charley -

  1. Condensate line leakage back into cabinet / controls
  2. Poor or No gluing on various joints of exhaust / intake
  3. Intake designed for outside, being inside in CONFINED size space
  4. Exhaust terminating outside too close to windows, ground, etc

Noted: list is growning your #1 is my # 2 my # 1 has not been identified as of yet. When we get done here we will have a good list for the newbes to go by:D

A few that I’ve seen include:
Exhaust/Intakes at the incorrect height above ground, check manufacturers instructions
Air intake taken from the furnace room, i.e. not run to the outside, makeup air for that room causing negative pressure…possible backdrafting of water heater, etc…
lack of condensate trap, to prevent backflow/bacteria growth, etc.
Condensate trap doesn’t run to a drain, just to the floor

Your #1,#2,#3 and #4 are covered in posts #1,#2,#3 and #4
not sure which issues will make Charlies list of #1,#2,#3 and #4 .

When both terminating at exterior, intake and exhaust too close together and/or exhaust below intake pipe.

Leaking condensate and dirty intake screen.

Actually a missing screen is even more common around here.

Still no one has listed my # 1, surely I am not the only one out of 9000+ that checks it;-)???

Check for pre & post purge.

Ya are getting closer but no cigar:p;-)

Nothing like a good belch after a meal eh ?