Correct way to test a Heat Exchanger?

[heatmehot]

So, what's the best way to test a Heat Exchanger? I hear you can do a combustion C02 test, fill it up with water and see if it leaks on the edges around the chamber or smoke bomb it. What's the correct way?

Thanks...

[2hot2coolme]

Simple way is by using a saltwater solution, spray it in the chamber, and take a blue flame torch to the registers and see if the flame changes colors...cheap'n'easy way but foolproof.

[ryan_the_furnace_guy]

Originally posted by 2hot2coolme
Simple way is by using a saltwater solution, spray it in the chamber, and take a blue flame torch to the registers and see if the flame changes colors...cheap'n'easy way but foolproof.

I am always looking to expand my knowledge on testing heat exchangers. This sounds like a good method. I would worry about doing damage to the heat exchanger though. Salt water?

[key]

2hot2

can you explain a bit more on this technique,do you run fan, why does flame change, what color will flame be?
thanx

[krd]

Test methods are like opinions, everybody has their own best method. In the city where I live the gas company uses a co detector that is calibrated every 30 days. I personally use the light method even though I own a CO meter. Mine was over $400.00. In my opinion the water method even though reliable is very time consuming. Do you have that kind of time on a Job? I have seen on post where they sprayed soapy water into the heat exchanger and turned on the fan and looked for bubbles. Keep in mind once the inside fan comes on the plenum becomes positive pressure so I'm a little confused on the salt water method.If you have a definite large crack it is usually easily visible with light thru it and every other method Is open to opinion. What if you say it cracked and they call another service company and they it isn't. No homeowner likes bad news. So I'm very cautious when I condemn somthing. I was only questioned once and the customer told me that he had been told the same thing several years ago and his buddy who is more than qualified to do this kind of work told him the serviceman was just trying to sell him a furnace. And I was full of -hit. His heat exchanger was fine. I signed off on my paperwork that I got visible light thru the crack and the furnace was considered unsafe for use. He is still using it and he isn't dead yet. It's not my house, I can only advise.

[cobraon]

When checking a gas furnace for CO2, I usually disconnect the blower motor and then cycle the burners until the high limit trips. By doing this, I know the heat exchanger is hot and the metal has expanded, plus this verifies the high limit is working. I then reconnect the blower and cycle the furnace again. I check at the closest supply register with a Fluke 210. If I get a positive reading I then get out my trusty halide torch and salt water bottle. If the heat exchanger is cracked and the salt water mixture enters the supply airstream through the heat exchanger, the halide flame will turn orange. So far,after 25+ yrs of testing this way(halide torch/salt water), every furnace I "red tagged" and changed out, did in fact have cracks/holes upon visual inspection.

[jacob perkins]

Originally posted by heatmehot
So, what's the best way to test a Heat Exchanger? I hear you can do a combustion C02 test, fill it up with water and see if it leaks on the edges around the chamber or smoke bomb it. What's the correct way?

Thanks...

We use canaries...but the SPCA frowns on that practice.

With a combustion analizer you can be certain of the problem or potential problems,and what to do to fix it.

[Carnak]

Checking HXs but were afraid to ask.

Mech Acc did an excellent post on this, it is in the FYI forum, one of the best posts in there.

http://hvac-talk.com/vbb/showthread.php?threadid=73546

[faith]

(Personal Opinion verses Professional Judgment) First and foremost, heat exchanger inspection is one of the most important professional duties a HVAC Technician is required to perform (my personal opinion). All furnaces fail, (typically the Heat Exchanger is the show stopper) it’s just a matter of time, that is a given. No homeowner wants to hear the bad news that is common sense. CO isn’t to be taken lightly http://www.epa.gov/iaq/pubs/coftsht.html

Don’t rely on here-say, the furnace vendor’s documentation needs to be carefully reviewed and more importantly understood. Premature failure is often due to inappropriate installation & setup and incorrectly sized (or installed) air distribution systems. Many other misunderstood parameters not adequately addressed will doom even the most robust equipment.

That said, I personally had the opportunity to attend a hands-on seminar given by Ellis Prach of Heat Exchanger Experts. The ACCA-National Capital Chapter in Savage, MD sponsored this event. Rather than promoting ACCA, I would personally suggest you see if Mr. Prach is scheduled to be in your area, if so please consider trying to attend.

http://www.heatexchangerexperts.com/

As for testing protocols, they vary greatly according to the exact type of heat exchanger (A.K.A. primary or secondary in high efficiency units). Each protocol has its place; it is your responsibility as a professional to know exactly how best to procedure under any given set of conditions.

This subject is the source of some heated Forum debate (which is in itself good) however owing to the delicate détente issues I (personal opinion) strongly suggest you invest a healthy amount of academic research into this subject lest you become involved it the “Heat Exchanger Scam” marketing techniques which have proven, for some in our industry, an effective revenue generator, albeit grossly unethical. Enough said.

My colleagues in other walks of life have consistently questioned me on this particular aspect of the industry, and for good cause. Please help your service area community and become highly skilled in this one facet of our very diverse industry. Residential HVAC needs knowledgeable; proficient and ethical champions, please join in and meet this challenge.

God Bless.

[faith]

Thank you Carnak
and Don
and Gary Reecher

Good Job!

[Carnak]

The credit is all due to Mech Acc aka Gary

[heatmehot]

Thank you all....that is a very good document. Question though....I had two seperate companies look at my furnace. One technician said my heat exchanger is leaking around the edges (water test), other technician did a combustion test and found no C02 leakage. Which test is more accurate??

Thanks....

[cem-bsee]

probably the water test is more accurate --

combustion analyzer depends upon the calibration of the meter, its accuracy at the read value, the placement of the probe with respect to the flue gas flow, the amount of flue flow

the training & experience of the tech --

but, the presence of CO is the problem

maybe your furnace design is such that slight amount of CO is drafted away --

[m1cowden]

how can salt water enter the supply air through a cracked
heat exchanger when the blower puts the heat exchanger under a possative pressure?

[gcastillo]

Originally posted by heatmehot
Thank you all....that is a very good document. Question though....I had two seperate companies look at my furnace. One technician said my heat exchanger is leaking around the edges (water test), other technician did a combustion test and found no C02 leakage. Which test is more accurate??

Thanks....

There may be a crack and not have CO not CO2 difference one is Carbon Dioxide CO2 the gas in question is Carbon Monoxide CO. What will happen if you do have a crack eventually it will get big enough where you will have an unsafe situation. Why wait for that to happen?

[heatmehot]

Well, for now there isn't a crack...just leaking on the edges of the heat exchanger. The heat exchanger is crimped all around. It doesn't seem like it is welded. By design...should there be a little leakage around the edges of every heat exchanger??

[wallynut]

You should have no leakage from any crimped exchanger.

[heatmehot]

Gosh....I don't know who to believe now. I had one technician come over and told me that even the new furnaces heat exchanger have some leakage around the edges. Is that true?

Thanks....

[krd]

I have had representatives from a major manufacturer inform me of the same thing. He said the little bit of leakage is no more dangerous than your wife cooking a turkey in the oven for 3-4hrs.

[hvac r us 2]

I usually don’t have the time to respond to long drawn out post but I felt this subject matter was important enough for me to put in my two cents.

The post by Mech is excellent explaining different methods available, but I would like to make some clarifications especially in regards to draft induced equipment.

First off, not all HTX leak CO. Induced draft furnaces are under negative pressure. A crack on these HTX can cause air to be drawn into the HTX instead of combustion products entering the air stream.

Make no mistake, all cracked HTX indicate a problem with the system!

As shown in Mechs post there are several different test methods available such as Lithium Bromide/Salt Spray, water testing, Tracer gas, Bore scope…and so on.

Let’s start with Lithium Bromide test, for most manufactures this is not recommended. Test involves spraying a solution directly into the burners, then checking the supply air plenum with a propane torch.
Lithium Bromide or other chemical salt solutions are highly corrosive. If you used it, and it didn’t leak now, it probably will in the near future!

How about internal water testing? That doesn’t even sound right does it? Filling each cell with water to see if it leaks? There are 8 approved methods of sealing a HTX including a “rigid pressed joint”. This seam is a rolled and crimped design that is gas tight construction not water tight construction. This method is used by many manufactures, and is not designed to hold water.

External water testing is performed by spraying water or a light oil mix on the outside and looking on the inside of HTX for leakage. Same potential problems as internal water tests.

Tracer gas method is an approved method by AGA. Typically tracer gas is 14% non-odorized methane. You inject it into the heat exchanger and check for leakage using a combustional gas leak detector. Works well for natural draft furnaces, works pretty well for 80 plus units but difficult to check secondary HTX on 90 plus units. The problem is in the testing process…

The seam on a “rigid press joint” is certified by CSA (Canadian Standard Association) formally know as AGA and CGA. The seams are gas tight due to the construction and assembly technique of the HTX combined with the negative pressure effect of the draft inducer.

In other words, just flushing a bunch of tracer gas into a cell can force a good HTX to fail the test. There is plenty of room for error…

Scopes work well but takes practice navigating, can be difficult to search out tight areas.
I still feel strongly that visual inspection on draft induced equipment can be very accurate and by many is a preferred method.

No matter what method you prefer good understanding of the equipment and common sense will be the biggest aid in identifying problematic HTX.

Since HTX either corrode or crack, the real question is…why?