Cracked HX and NO CO!!

Glenn Harrison · March 2003

You might want to talk about those CO readings with Rudy Leatherman of Bacharach Training at

rudy@eurekanet.com

I attended his combustion class last fall and he talks about doing a three part combusiton test. Startup, running, and shutdown. Many times these tests and documentation can tell you when a unit is starting to malfunction. I believe one example he gave was of a unit that suddenly had completly different readings on shutdown than in previous years, turned out the fuel oil pump cutoff had failed.

Mark Hunt · February 2003

How does this happen?

We removed and replaced an oil fired FHA furnace today that was "suspected" of having a cracked HX.

Once we took the jacket off we found a HUGE split right over the burner and several smaller holes in the HX.

I tested this unit before hand with a digital CO analyzer and got 0 ppm CO. I tested the exhaust and got 45 ppm air free, but nothing in the air stream.

We finished late but I will post pics of this tomorrow.

It had to be like this for years!

BTW, have any of you tested CO readings AFTER a burner shuts down?

If you haven't, give it a try. You will be suprised at what you find!

Mark H

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Steamhead · February 2003

Post-shutdown CO

I've noticed that too, Mark- CO goes up. I think this is because the air supply slackens off quickly while there's still some fuel in the process of being burned. This seems to be very common on gas ovens.

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Mark Hunt · February 2003

SCARY

I was working with Mark yesterday doing the changeout. I wish we had the digital camera with us. When the jacket was stripped away there was some major openings on the heat exchanger. This did not happen overnite, it was "serviced year after year by the same company. It always amazes me why there are not more serious accidents happening out there. Why was this not caught years earlier? I think this is the difference between a $65.00 special cleaning and a $150.00 check every thing cleaning. I am pretty positve that I would not want to gamble with my life for a $85.00 savings.

Mark Hunt · February 2003

Testing

You are correct. We test start up, running and shut down.

A few weeks ago we installed another oil unit and watched the CO climb to 1200ppm when it shut down! It was caused by unburned fuel in the combustion chamber. The unit needed some adjusting to get it to fire so there was a bit of #2 in the combustion chamber.

You will see the same thing when you test other equipment as well. I tested a gas stove the other day and got a spike of 25ppm on start, dropped to 6ppm after 3 minutes and jumped to 45ppm on shut down.

I will take a pic of that HX, I haven't taken it to the salvage yard yet.

Mark H

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Glenn Harrison · February 2003

I know what you mean about other appliaances.

I had an oven earlier this year that ignited at 200ppm and worked it's way down to 40ppm within a minute. Told 'em to get it professionally cleaned and tested. CO readings a little high for my tastes.

Mark Hunt · February 2003

Gas ovens

scare me. I do not care what the code says. Anything that produces CO should be vented, PERIOD!

We did an energy audit at a customers house a few weeks ago. The HO had knocked a wire off of one of his zone valves causing it to stay closed. The glycol in the system had not been checked since it was put in 10 years prior!! No freeze protection for the system at all and the first floor zone froze. He was convinced that the pipes were frozen in the kitchen area so he started his LP gas oven and opened the door!! I walk in with my Pro-120 and get instant CO readings and I see the oven door open. "WHAT THE HELL ARE YOU DOING?!?!?" I asked. He told me he was trying to get heat into that area in an attempt to thaw the pipes. I made him shut it off. Now that oven could produce up to 800ppm CO and be code compliant. Everybody could be dead, but no one is to blame? BULL!!!

We have a ZERO tolerance policy for CO at our company. If it is spilling even a little it gets shut down. Things can change and change FAST. I sleep better at night knowing my customers will wake up in the morning!

Mark H

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Unknown · February 2003

Inspector Camera

should be another tool in every test package. A hole in the heat exchanger will not necessarily make CO.

Nothing like an infrared picture along with water test on HX.

Unknown · February 2003

CO after shut down

is the reason many furnaces and boilers have pre-purge and post purge on combustion air blower.

By the way have any of you ever had CO explode on you???

Lower Explosive limit 12.5% upper explosive limit 74%, I have had this occur a couple of times with spark ignition systems. I had a Trianco Heatmaker blow so bad it blew a hole in the coil.

CO specific gravity .97 very close to air which is 1.0 it lingers and lurks and KILLS.

You are all doing good every one is learning all the wild stuff that can happen.

How about those Jenn-Air grills????

Unknown · February 2003

Test - Cold-Hot-Shutdown

this is what is nice about electronic testers we can monitor CO and its behavior.

Same way the house environment should be tested by the way test three times.

Mark Hunt · February 2003

MANOSCHEVITS TIMMIE!!!!!!

Darin and I are looking to buy a camera for just that purpose. We talked about it today.

The more I see out there, the more I realize how much MORE I need to know!

Any suggestions for an inspection camera?

Mark H

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Mark Hunt · February 2003

pics

Here they are folks.

Mark H

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Unknown · February 2003

I recommend for a camera

"The Inspector" from Shamrock Industries, phone # 1-888-814-8540

FAX 1-630-690-0297

They will send you a video and a packet explaining how the camera works. Everyone I know who has purchased one says it pays for itself in the first month in new installs alone. Not to mention saving lives of your customers which I think wins them to you for life.

Unknown · February 2003

Rapid cooling of flame

called "quenching" will cause an increase in CO for a short period of time on shut down. Ovens and water heaters have a tendency to do this also some space heaters.

Steamhead · February 2003

I test the same way

it's the only way to get a clear picture of what's going on thru the entire cycle.

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rob · March 2003

Tune-up

Just a little suggestion, when I perform a tune-up on an oil furnace with cleanout access covers I leave them off until I service the burner. Then I do the CET with the covers off and look inside for any glowing or even orange cracks. Turn off the drop light and if there is a crack you will see it. Rheem ROBB are easy to check that way. Old Heils have the back panel that is removable and have a gasketed flange back there that can warp. Another thing I saw once, I #1 smoke without the fan and then a clean smoke dot when fan came on- the Heil flange had opened up. The may been the cause for the lack of CO readings on your job- the fan was diluting the sample? Like Rossanna Rosanana Dananan sez-- it's always something!

Rick Price · March 2003

share another CO moment.....

about 10 years ago when CO knowledge seemed basically hear-say, I took a oil burner combustion class. The instructor told the students in the class "with oil if you have CO, you will have an odor". I learned this is MOST Definitely NOT true. Case in point- a few years ago, I had what I thought to be a cracked heat exchanger - so I dirtied up the oil burner flame and started doing CO tests. The unit showed ambient CO readings - until the blower stopped. With the crack in HX, the excess blower air was just the part of the combustion equation to give the false readings. I don't think today there is just one check for CO - you have to pull out all the stops; shut things down - fire others up, run the unit in the worst possible condition then check again.

Steve Ebels · March 2003

Mark

The situation you described is not all that uncommon and when you think about it you can see why.

You have a chimney creating a negative pressure in the firebox and the blower (when it's running) creating a positive pressure around the outside. This tends to keep the flue gases confined inside of the combustion chamber. I've run into this probably a dozen times at least and it puzzled me too until I thought about the air pressure differential in that area of a furnace.

This is not to say it's not dangerous!! There are a LOT of situations that can take this from benign to catastrophic in a heartbeat. Also what happens when that chunk burns through and you have the flame directly in contact with the air side of the system. I don't even like to think about it.

Mark Hunt · March 2003

Yes sir

> The situation you described is not all that

> uncommon and when you think about it you can see

> why.

>

> You have a chimney creating a negative

> pressure in the firebox and the blower (when it's

> running) creating a positive pressure around the

> outside. This tends to keep the flue gases

> confined inside of the combustion chamber. I've

> run into this probably a dozen times at least and

> it puzzled me too until I thought about the air

> pressure differential in that area of a furnace.

> This is not to say it's not dangerous!! There are

> a LOT of situations that can take this from

> benign to catastrophic in a heartbeat. Also what

> happens when that chunk burns through and you

> have the flame directly in contact with the air

> side of the system. I don't even like to think

> about it.

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Mark Hunt · March 2003

Amen Steve

I probably should have mentioned that I watched the O2 readings jump when the fan came on. The unit was drafting but as we all know things can change very quickly.

It is amazing what you will find if you just look!

All the best!

Mark H

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Steamhead · March 2003

Here's another good one-

Hoffman Vapor system with original style Differential Loop. CO detector in boiler room sounded. Owner called gas company who found his boiler was cracked above the waterline. Then he called us to get a bid on a new boiler.

But where was the CO coming from? The vent on the Differential Loop!

That vent was a vacuum type- Hoffman #6 which was way too small for that system. It would let air out but not in. When the steam in the system condensed, it would pull flue gas in thru the crack in the boiler. On the next cycle, that flue gas would go out the vent on the Loop and set off the CO detector.

I replaced that vent, and another one way out at the end of the system, with Gorton #2 vents that will not pull a vacuum. Got the boiler CO down- it was overgassed and piped wrong, sound familiar?

We haven't changed the boiler yet- owner wants to wait for warm weather- but the CO is gone. This is another reason not to use vacuum vents on steam systems.

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Cracked HX and NO CO!!

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