bad heat exchanger

jaybee

How can u tell if u have a bad heat exchanger ive havent come across one yet?

Mark Hunt

Assuming you are talking forced air?


You need a good combustion analyzer.

Top two:

Test in the flue and watch the O2 number. If it changes when the blower comes on, you have an issue.

A visual inspection, but you can't always see the entire HX without dismantling the furnace.

Other tests include:

Watching pilot lights, I personally do not trust that test as I have never seen an air tight blower compartment.

Testing for CO in the air stream. I don't trust that one either. You could have a cracked HX and still get no CO reading in the air stream when the blower comes on. You may only get CO in the air stream before or after the blower shuts off.

Soot around registers is an indicator of a potential problem.

Best bet though is with a combustion analyzer. My Bacharach Fyrite Pro's are worth 100 times their weight in gold. They NEVER lie.

Mark H

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jaybee

bad heat exchaner

Can u explain to me how getting a change to no co2 reading when the blower comes on would indicate a bad or cracked heat exchanger and soot on the registers?

Constantin

I'm just a homeowner but...

> Can u explain to me how getting a change to no

> co2 reading when the blower comes on would

> indicate a bad or cracked heat exchanger and soot

> on the registers?

Constantin

I'm just a homeowner but...

if the combustion gases change when the blower motor for the house duct system comes on, then you know that the duct blower motor is affecting the combustion. The only way for that to happen is for the HX to have a crack in it.

Soot on the registers would be the result of a similar issue. You should never find soot on the registers but it may be derived from bad combustion byproducts finding their way into the house via cracks in the HX. In the limited reading I have done on the subject, sooting around the house is much more frequently the result of either cigar smoke or (worse!) the usage of scented candles.

Hence, my better half does not get to put on the "mood lighting" very often. It's too much of PITA to clean up the mess that eventually settles throughout the home. I understand that some candles burn more cleanly than others, but there is no label to indicate the relative "soot-factor" so I don't like them at all.

Mark Hunt

O2 not CO2


A rise in the oxygen reading would indicate that air is being pushed into the exhaust through a crack/hole in the HX.

Hope this helps.

Mark H

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DaveC

Just wondering...

if air (from the blower?) is being pushed into the exhaust, how is soot going against that flow to get out the registers?

Mark Hunt

It wouldn't


unless soot was being pushed out of a flue pipe and sucked into the return air and then sent into the home.

Mark H

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DaveC

But isn't that...

the circumstance that Jaybee is describing?

Mark Hunt

My bad!


Re-read the post.

Thanks Jim!

Mark H

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DaveC

Hey, that's what PITAs like me...

are here for! Now, can you generally describe what the typical pressures are on each side of the heat exchanger? Are they both negative? If so, which is a larger negative value? Or does it vary?

tommyoil

Provided the furnace is clean and the chimney is in good working order, with the burner running, try an overfire draft test before the blower comes on. Should be neg. Then after the blower comes on test again. Pos. pressure w/ blower on could indicate a problem. OR you can cap the flue AT the furnace breech and turn on the blower(without the burner running of course) and check for positive o.f. readings. Pos. draft reading o.f. with the blower only running could mean its time to go hydronic. But of course, nothing beats a visual of the hx. Is there such a thing as scorched air heating help.com?

Steamhead

Here's a good place to start

http://www.thesheetmetalshop.com/pn/

I think there are others, but Bud (webmaster) is a real good guy.

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GaryDidier

Candle Soot

Gel candles are the worst!

Gary from Granville

GaryDidier

Combustion Analyzer

Jaybee,
You should sign up for a class on combustion theory and train on the use of a computerized analyzer. Rudy from Bacharach gives an excellant class.

Gary from Granville

Robert O'Connor_6

Soot

has way too much personality!

I suspect it will migrate anywhere it can before the blower comes on . In that scenario

I like to use my bacharach to test hx too!

Regards

Robert

ME

ernie_3

an old timer told me...

put a shot glass of spearmint in the combustion chamber,
SHUT THE SERVICE SWITCH OFF! do not run furnace or blower.
over a couple of days if the pleasant smell of spearmint wafts through the house hx integrity is breached.
Some co's caryy a 'video snake' to visually inspect the hx.
I've had good luck w' draft tests, overfire then overfire draft test w' the blower running.

Steve Miller

cracks

Remember just because you find no CO, doesn't mean it's not cracked. Here In El Paso CO. in Colorado Springs, there are no acceptable cracks allowed. It's a sign the intergity of your furnace is shot and time to replace. If your furnace is over ten years old anyway and not at least an 80% you should replace in my opinion. An Amana is a good choice because of their stainless steel exchanger construction and lifetime warranty. I highly recommend a 90+ furnace because with the rising fuel costs you can recoop the investment pretty quick ans with the sealed combustion it really cuts down on infiltration.

Also, check out heatexchangerexperts.com I went to Ellis Prach's class and learned so much. He was considered a crook here because he condemded so many furnaces with cracked heat exchangers and it turns out he was right all along. It's a good hands on class because he has about 50 furnaces on display so you can see up close and personal.

Steve M

J.C.A._3

Steve,

> Remember just because you find no CO, doesn't

> mean it's not cracked. Here In El Paso CO. in

> Colorado Springs, there are no acceptable cracks

> allowed. It's a sign the intergity of your

> furnace is shot and time to replace. If your

> furnace is over ten years old anyway and not at

> least an 80% you should replace in my opinion. An

> Amana is a good choice because of their stainless

> steel exchanger construction and lifetime

> warranty. I highly recommend a 90+ furnace

> because with the rising fuel costs you can recoop

> the investment pretty quick ans with the sealed

> combustion it really cuts down on

> infiltration.

>

> Also, check out

> heatexchangerexperts.com I went to Ellis Prach's

> class and learned so much. He was considered a

> crook here because he condemded so many furnaces

> with cracked heat exchangers and it turns out he

> was right all along. It's a good hands on class

> because he has about 50 furnaces on display so

> you can see up close and personal.

>

> Steve M



But have you ever dealt with an "old yankee"?

Your reasoning would be tossed out like an old beer can .

Try to sell your "theory" to someone in this area, and you may as well put a gun to your head...cause you'll DIE before they give into an overall assessment like yours.
One class .....does not make you an expert.(trust me)
If I was trying to condemn every warm air system I came across

J.C.A._3

Steve, Ever met an old Yankee?

Colorado folks may buy this, but here in the Northeast, not a chance.

Your reasoning would be tossed out like an old beer can .

Try to sell your "theory" to someone in this area, and you may as well put a gun to your head...cause you'll DIE before they give into an overall assessment like yours.
One class .....does not make you an expert.(trust me)
If I was trying to condemn every warm air system I came across,I could fault them in seconds. Air is a crappy heat transfer medium to begin with. Seldom is ther a need for furthur explanation, but I won't try to "hard sell" a customer on a "preachers terms".
Get yourself a way to make the decision. Take lessons from ALL teachers and make a plan for yourself.

The post you made makes you sound like you're "pigeonholed" into 1 mindset.

Think for yourself. Learn as much as you can. THEN, make personal and INFORMED decisions.Please don't go buying a salesman pitch. It makes you look narrow minded, and the point here is to expand you and your customers options, based on your knowlodge, not preferences.Think about it. Chris

Ken D.

Heat Exchnr.

Draft, CO2, O2, flame appearance,all checked before and after blower and smoke candles and peppermint are all good. It is a good idea to allow for a long run time to give the exchanger a chance to heat and expand. Be careful! I once had a customer who had odors. I used all the methods to check and found no sign of cracks at all. On the 3rd call, I opened the plenum and found a large hole in the top of the exchanger. It was in just the right area (toward the rear) where the testing did not reveal it. The unit was in the closet and access to the rear was impossible. It was an eye opener. When in doubt, check it visually.

Steve Miller

Steve Miller

in response

Chris, I'm not sure what you meant by my 'theory'? I did offer an opinion on old furnaces on my post but I would never tell it to a customer. If I'm on a service call for a clean, tune and inspection and find a cracked heat exchanger, I have to file an unsafe condition report to the local jurisdiction. I didn't make up the rules. I don't try to 'hard sell' a new furnace and say they're all gonna die from CO if they don't buy a furnace from me. It's my job to present my customer with information that they've paid me to do. Most bad heat exchangers are the result of oversized furnaces, poor duct work, not changing filters, limit settings, etc. I give my customers the info and they can make their own decisions, chances are, they're not going to buy a furnace from me anyway being the bearer of bad news. If I don't tell them of problems and another company comes in and note they have problems, I look bad. I have to at least put it in writing, too many lawyers out there ya know. If you don't want to tell your Yankee customers they have a cracked heat exchanger, fine, I hope you sleep well at night.

This is my 25th year in the business and one class did not make me an expert as I learn something everyday in our business. Forced air doesn't have to be crappy as you said. A correct sized furnace with properly sized duct work and air filtration can be a nice system. Not everyone can have the hydronic heat that we love to promote and it's our job to help everyone. I did take offense of your post directed toward me but I'll let it slide because sometimes things get lost in translation. I'm not the best at typing out my thoughts so maybe I came off differently.

Thought about it, Steve

Unknown

Heat Exchanger Tests PAST AND PRESENT

SMOKE TEST

With the flue outlet open and with the draft hood relief opening and burner access opening blocked, a smoke candle is ignited in the heat exchanger. A large quantity of dense smoke is produced, and the air side of the furnace is visually checked for signs of smoke which would indicate a leaky heat exchanger

SPIRIT OF PEPPERMINT

Needs two people one in contact with peppermint the other isolated away so as to not pick up any smell of peppermint. Spirit of peppermint is placed in pill capsules from local drug store (drug store will do this for you). Person 1 places capsules on the burners and brings the furnace on, person 2 is upstairs smelling at registers for peppermint smell. Smell of peppermint says HX is cracked.

SALT SPRAY

This method emplys a sodium salt/water solution which is sprayed into the combustion chamber, and a propane torch is used as a detector on the air side. If the blue flame of the torch turns yellow, this would indicate the presence of sodium ions in the air stream and a leak in the heat exchanger.

Refrigerant has also been used as a tracer gas along with halogen leak detector to sense air side of the system. Odorants and even a flourescent solution with an ultraviolet light as a detector have been employed.

A critical problem with these methods is the fact that it is almost impossible to construct a leak tight heat exchanger in the first place. This means that some tests could be too sensitive and detect an inconsequential leak in a joint or seam that is within acceptable leakage rates according to industry manufacturing and safety standards. There have therefore been replacements in the past that were not necessary.

TRACER GAS TECHNIQUE

To eliminate "false" indications of a safety problem, the gas industry has introduced a tracer gas/detector system that features a combustible gas detector with a minimum threshold level alarm. The test, in other words, would only detect cracks and leaks large enough to be of concern.

The "Tracer Gas" is a special blend of methane gas and nitrogen which cannot become combustible when mixed with air. The detector is specially calibrated with a calibration gas.

Very basically, the tracer gas is introduced into the combustion chamber with the furnace off. The probe on the detector is inserted into the duct plenum chamber as close to the top of the heat exchanger as possible. Like a Geiger Counter the gas detector will give off an audible series of "clicks" when detecting low concentrations of the tracer gas.

THE INSPECTOR CAMERA

The ultimate test today is with an infrared camera which is just about the best test as it is visual and has several special actions to contribute to accuracy.

For lack of direct visual confirmation using a Combustion tester 02 test as someone else mentioned is close enough.

The truth is the visual is the best test of all but always very difficult. A good mirror and strong light looking up into the sections can find many extreme cases of HX damage.