Scorch Mark on Furnace

I found this on my afternoon inspection today. As per my normal routine, I fired up the furnace at the end of the inspection. But, I noticed this scorch mark during my visual inspection of the furnace. The furnace fired up and was running for about 5 minutes before I snapped this image (back side of gas fired forced air furnace).

Funny thing is the the Agent broke out the sellers disclosure and it had a reciept from a HVAC technician that clearly indicated that the furnace was functional and safe to operate. How could the Tech have missed the big scorth mark in the back of the furnace is beyond me.

Anyways, any ideas as to possible cause? Cracked heat exchanger, maybe? For you HVAC Gurus out there :slight_smile:




Would a cracked heat exchanger cause that?

We must be on the same wavelength :slight_smile:

I edited my original post to include “Cracked heat exchanger, maybe?” while you were posting your answer.

Let’s see what anyone else come up with.


What type of furnace is it? A picture would help.

Gas fired forced air furnace (Lennox).



The bottom of the heat exchanger is just behind that scorch mark on the back.

It looks like and old furnace.
I wonder how the HVAC “tech” “tested” the unit. :roll::roll:

I was just thinking that sure looks like an old unit…I’d call for a evaluation by hvac specialist…jim



I can read Rick…i’m just saying what i would put in my report…maybe that first guy was not all seeing…I sure would not just say ok to that unit…jim

You know guys as one gets older other things do not appear as old either. Has anyone ever really observed an old furnace I will show you one from today.

Kevin you may not have a cracked exchanger just yet but the proballity is very high. The unit could also be staying on to long for various reasons and the high limit switch not working. You have a problem there should be no heat marks on the outer shell of the furnace cabinet. I think you can wear a feather in your cap on this one. HVAC techs do not walk on water they can miss things also I see their work all of the time.

Looks broke to me! :wink:

You should be able to look in the burner compartment and see this type heat exchanger.

Was the elevation about the same as the burners?

The heat exchanger could have been worked on in it’s past life and is touching the back of the cabinet.

I would put my $$$ on the cracked HE.

Time to get out the bore scope!

Well, it looks like I’m going to be called out on this one. Got a call from the agent a little while ago. They want me and I quote “my camera” to return to the property on Monday. The sellers want to have the HVAC tech that conducted the inspection on site.

I’m up for the challange!!

Thanks for the replies.



Sorry if I implied that - no offense meant.
This is quite clearly something that needs a tech (who knows what’s going on).

Ironic that they want the original guy back out there.

Love the photos. Which FLIR cam were you using?

Also, what’s the resolution? Nice picture.