Correct term for flame extended beyond side of burner? - InspectionNews

Michael Thomas · #1 (**permalink**) 07-15-2008, 07:25 AM

What is the correct term for the condition where the flame in a GFAF extends past the side of the burner and impinges on the sheet metal burner housing, and what is that housing properly called?

(Yes. I know the furnace is toast. You can feel the roll out at the draft hood when the blower kicks on. I just want to know how to properly describe that flame impingement.)

- Thanks

Scott Patterson · #2 (**permalink**) 07-15-2008, 07:30 AM

I would call it flame roll out. Chance are though that your client would not understand that term so I might simply just say that the burner is not burning properly.

Markus Keller · #3 (**permalink**) 07-15-2008, 07:39 AM

I've never heard anyone in the trades call it anything but 'flame rollout'. Like Scott said you'll probably have to do some splaining to the client.
Flame rollout can occur from several reasons such as back drafting flue, negative pressure in room from other appliances and rusted out heat exchanger.

David Banks · #4 (**permalink**) 07-15-2008, 07:44 AM

I had a similar situation a few years back. Talked to HVAC guy at coffee shop the next day and he says it is really a breach of the heat exchanger. Talked to the buyer in the spring as I went back to check his exterior GFI'S as there was 3-4 feet of snow. He said the Furnace guy he had look at it says it is fine. I told him I find that hard to believe and could be safety issue. He said I am going to change it out this year anyway. Hard to believe furnace guy would give ok.

Michael Thomas · #5 (**permalink**) 07-15-2008, 07:50 AM

Thanks.

I've always though of "flame rollout" as often intermittent condition occurring at and beyond the front end of the burners. This is a continuous, steady flame at the side of the burner where it enters the inner sheet metal casing of the furnace. I don't intend to get that detailed with the client "This furnace is beyond the end of it's expected and safe operating life and requires immediate replacement" is what they need to know. I just wanted to know if there is a specific term for that steady flame-to-the-side so that I can accurately describe it to HVAC service personnel if I ever need to.

David Banks · #6 (**permalink**) 07-15-2008, 07:54 AM

Quote:

Originally Posted by Michael Thomas

Thanks.

I've always though of "flame rollout" as often intermittent condition occurring at and beyond the front end of the burners, this is a continuous, steady flame at the side of the burner where it enters the inner sheet metal casing of the furnace. I don't intend to get that detailed with the client "This furnace is beyond the end of it's expected and safe operating life and requires immediate replacement" is what they need to know. I just wanted to know if there is a specific term for that steady flame-to-the-side so that I can accurately describe it to HVAC service personnel if I ever need to.

I often wondered that myself Michael.

Michael Thomas · #7 (**permalink**) 07-15-2008, 08:25 AM

I seem to be attending having a bad heat exchanger festival this month - likely, two out of three in this house alone! - other times I can go months without encountering anything suspicious.

And all these houses have been occupied, and none of the occupants are reporting adverse health effects.

Of course I'm going to continue to call out every one.

But I am beginning to wonder if compromised HEs are anywhere near as dangerous as disconnected vent pipes or situations where exhaust is entering the cold air return stream - I've read account of injuries and deaths from the latter two, but i don't remember ever reading of the same from a HE leak.

David Banks · #8 (**permalink**) 07-15-2008, 09:14 AM

Quote:

Originally Posted by Michael Thomas

I seem to be attending having a bad heat exchanger festival this month - likely, two out of three in this house alone! - other times I can go months without encountering anything suspicious.

And all these houses have been occupied, and none of the occupants are reporting adverse health effects.

Of course I'm going to continue to call out every one.

But I am beginning to wonder if compromised HEs are anywhere near as dangerous as disconnected vent pipes or situations where exhaust is entering the cold air return stream - I've read account of injuries and deaths from the latter two, but i don't remember ever reading of the same from a HE leak.

I think your right. Most heat exchanger leaks I have seen pics of are small rusted holes/cracks.

Scott Patterson · #9 (**permalink**) 07-15-2008, 01:02 PM

One of the reasons folks don't suffer from the effects of a cracked heat exchanger is that it takes a good size hole or crack for the flue gases to enter into the air stream. Most of the time and one of the reasons that the flame is wavers or fluctuates is that air is being sucked into the heat exchanger and not the other way around. The outside of the heat exchanger is under positive air pressure so it will push air into the crack on the heat exchanger.

At some point the crack or hole will be too large and the reverse will happen, and then this is when folks die!

DavidR · #10 (**permalink**) 07-16-2008, 02:22 PM

Quite a bit of misconceptions and assumptions about heat exchanger cracks and CO poisoning being posted on this thread.

The scenario you are encountering in your first picture Michael is due to the gas crossover of the inshot burner allowing the gas to burn outside of the last burner on the manifold.
It is not a rollout condition.

This is usually found with a unit that has weak draft in the flue or a weak draft inducer.
Combustion testing of the furnace would help to identify any other problems.

If all checks out okay just clamp the crossover gap down on the last burner with a pair of pliers to stop the flow of gas outside of the burner.

BARRY ADAIR · #11 (**permalink**) 07-16-2008, 05:48 PM

Quote:

Originally Posted by Michael Thomas

the sheet metal burner housing, and what is that housing properly called?

- Thanks

Are you referring to the heat shield or one of these others?

bruce m graham III · #12 (**permalink**) 07-16-2008, 06:32 PM

The burner on the left is defective, there is a built in gas path for the pilot flame to ignite on a call for heat. If you looked close you would see that the flame is coming from the stamp sheet metal of the burning.

Eric Barker · #13 (**permalink**) 07-16-2008, 06:38 PM

Michael,

The term that you may be looking for is over-firing which would not be the same as rollout.

DavidR · #14 (**permalink**) 07-16-2008, 07:48 PM

The easiest way to determine if that is occurring from an overfire condition is from combustion testing.

CO over 100 PPM, low O2, high stack temperature and a high supply plenum temperature combined are a good sign that overfiring is occurring is occurring in a furnace.

Michael Thomas · #15 (**permalink**) 07-21-2008, 11:19 AM

Seller had an HVAC tech out to look at a 25+ year old GFAF furnace I inspected last week, and the buyer forwarded me the following, forwarded from the seller's broker.

"They brought in Bart from American Weathermakers in Northbrook. His report (attached) states that they could not find cracks inside the exchanger with a fiber optic viewer. It looks like they found 2 cracks in the "face plate bisket?" (I couldn't read this part).

Therefore his recommendation is that it is safe to operate but is old and needs replaced."

Just wondering what the "face plate bisket?" could have been.

------------------------------------------------------------------------------------------------------------------------

IMO this furnace "is safe to operate but is old and needs to be replaced" in the same sense that that "a DC-3 with 80,000 hours on the airframe is safe to operate but is old and needs to be replaced".... but that's another story....

Michael Thomas · #16 (**permalink**) 07-21-2008, 11:23 AM

And thanks for all the responses.

Bob Harper · #17 (**permalink**) 07-21-2008, 11:38 AM

Michael, the problem, as described here was regarding the burner ports--not the HX. Did he inspect the burners? The burners should have been removed, photographed and inspected. If still serviceable, they should be cleaned and reinstalled after the HX is then inspected along with the venting. Once put back together, he should have run a combustion analysis and observe the burners while firing. Cracked burners can cause a host of problems and must be corrected before this unit is fired again.

As for your terminology, since it has not been determined to be true flame rollout as from a vent obstruction, you could refer to it as "fugitive flame with impingement" or some such.

HTH,
Bob

DavidR · #18 (**permalink**) 07-21-2008, 01:34 PM

Quote:

Originally Posted by Michael Thomas

"They brought in Bart from American Weathermakers in Northbrook. His report (attached) states that they could not find cracks inside the exchanger with a fiber optic viewer. It looks like they found 2 cracks in the "face plate bisket?" (I couldn't read this part).

Therefore his recommendation is that it is safe to operate but is old and needs replaced."

Simply amazing!
The guy looks at the furnace and declares it safe because it has no cracks.

Still such a long way to go.

Might not be a bad idea Michael to state that the safety of the appliance has not been verified by the HVAC guy as this can only be done through a thorough combustion analysis and draft interference test.
I wish I was good enough to determine how safe an applince was with just a visual.