Cracked heat exchangers

gary_6

On oil fired warm air units how can I tell if customer has a cracked heat exchanger?

Mark Hunt

Cracked HX


You could use a combustion analyzer and watch the O2 reading when the blower comes on. If you see an increase in the O2, you very well may have a cracked HX.

Testing for CO in the duct while the unit is working is another way, but it isn't fool proof. Of course if you get even a sniff of CO there, the furnace is finished.

A visual inspection can be difficult unless youi plan on removing the entire jacket. I have done that, and it blew the customers mind!

Mark H

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Leo

Testing heat exchangers

The suggestions given are all good. We also use smoke bombs made for this purpose, if somoke comes out of the vents in the house you have a bad exchanger.

Leo

sootmonkey

none

An oily rag is a cheap smoke bomb. This was told to me by an "old timer". Any Soot at the resiggisters? ( been chillin with a couple of cold wons sorry for spelling) Start with a cold unit..ie T stat not calling, fan and burner not running, service switch on. Jump out TT. After unit fires watch flame with inspection door open. Wait for fan to come on. Watch flame when fan comes on. BE CAREFULL WHEN DOING THIS. DO NOT STICK YOUR SMART, ALL KNOWING, FACE IN FRONT OF INSPECTION DOOR WHEN DOING THIS. Ask me why :} If flame fluters or changes in any way suspect a bad x-changer

Dennis - Reliable Services

If the draft changes when the fan comes on this is also,

an indication of a crack in the heat exchanger. Soot formation is also an indication.

Arthur

Cracked Heat Exchangers

What I do is temporary block up the flue with rag, close the burner damper Then put a digital manimeter in the a small hole in the burner veiwing hole and watch for a change in pressure when you manually switch on the main fan,
A cracked H/E is not as dangerous as it sounds as the main fan pressure is well above the pressure of the burner fan, So the main fan will tend to blow into the fire side rather than the other way around. Of course during preheat there will be some leakage out of the H/E into the air ways Before the main fan starts up.But this usually well diluted when the main fan starts.
How many cases of CO poisoning have there been from a leaking H/E ? I looked though the latest accidental home cases and couldn't find any in the last 5 yrs.
I had to condem one the other day as it was an old klear kleen burner which is suppose to run on mixture diesel and kero and the tanker outfit will only supply diesel not kero/diesel and the burner didn't like only diesel and started to smut up the house.
However there was no problem with CO poisoning. only smuts in over the furniture.

Mark Hunt

Sometimes


but not always.

CO poisoning is probably the most mis-diagnosed of all poisonings.

I have seen instances where the HX was burned through and yet no CO was found in the air stream, in just as many other cases I have detected it.

If a cracked HX is not a CO danger, why bother replacing them?

Eventually the CO WILL find a way into the home.

Mark H







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gas man_3

On heat exchangers ,I'd have to agree with you - if you find a crack, it needs to be replaced ! period- how can you tell a customer that you found a crack (or not tell them ) and leave it on, whats that exchanger look like 6 months from today ! Bottom line, wasn't designed with that crack, when furnace is on and running , heating to full temp constantly cause they don't change the filter -it gets bigger and bigger - today ,you get no c o readings -they get a cat - cat hair blocks air shutter - no we're making high levels of co - how big is that crack today !

GaryDidier

cracked heat exchanger

I agree with Mark Hunt. Usa a combustion anylizer with the burner running and let the readings stabilize.When the blower comes on the positive pressure will force air into any cracks or holes and will either increase 02 or dilute CO2. This test has never failed to find a bad exchanger.Besides the life safety issue a hole or crack makes it impossible to properly set up the burner because of the changing air characteristics.

GaryDidier

cracked heat exchanger

I agree with Mark Hunt. Usa a combustion anylizer with the burner running and let the readings stabilize.When the blower comes on the positive pressure will force air into any cracks or holes and will either increase 02 or dilute CO2. This test has never failed to find a bad exchanger.Besides the life safety issue a hole or crack makes it impossible to properly set up the burner because of the changing air characteristics.
Gary from Granville

Arthur

Cracked Heat Exchangers

1) I NEVER said any thing or even hinted that I would not inform the client(customer) about the results,After all it's the customer's call. So why accuse me of not telling them.
2) If you have set the burner up it should be producting very little CO any way, The last gas burner I did had 11ppm CO in the flue gas, Hardy enough to get excited about.note this was on a boiler not a furnace incase I get accused of that.
3) What about direct fired burners where the fire burns into the air stream
4) Nobody produced any figures of any one carking it from co from a cracked H/E.

Mark Hunt

Sorry


I will post more if you like,

Elderly Couple and Their Two Sons Found Dead in House, Faulty Furnace Suspected
The Associated Press Published: Oct 28, 2002

WOODBRIDGE, N.J. (AP) - An elderly couple and their two sons were found dead in
their home Monday, possibly from carbon monoxide poisoning, authorities said.
The four may have been dead since Thursday, the day they failed to turn up at a
family event in Pennsylvania, relatives told police. The bodies were discovered
after relatives sent someone to the house to check on them.

The furnace at the family's two-story, stone-fronted house appeared to be faulty
and the chimney was blocked, Woodbridge Mayor Frank Pelzman said.

Autopsies planned Monday and Tuesday were expected to pinpoint the cause of
death.

Police declined to release the victims' names until family members could be
notified.

Mark H

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Arthur

Cracked H/E

So, It didn't say that the furnace had a cracked H/E all it said was it was faulty, How was it faulty? Even a perfectly good furnace if the flue was blocked would cause problems.
Over here the return into the furnace is NOT allowed to draw from the same area as the furnace fire for this very reason.
Have you any more details?
Was it a gas furnace or an oil fired furnace? When was it last maintained?

Art Pittaway

Roll out switch

should have shut down the furnace if it was working. I don't trust them and I know they get bypast and if the flue was partially blocked and didn't get the sensor hot enough it wouldn't open. That may be the malfunction. Damn shame!

Arthur

Cracked H/E

The old gas furnaces didn't have rollout switches, As they were mostly atmospheric burners with a DDD so any blockage would have caused the products to rollout the DDD, If it rolled out the front you would have thought it would have smothered the flame out any way.
Gas burner are more dangeous than oil burners in this repect as an oil burner doesn't product the CO a gas burner does (or can do). Which is what we started discussing in the first place.

Mark Hunt

How many

oil burners have you checked sir?

I have found more than I can count that were in excess of 1000ppm.

I posted the wrong story the other day, too late now but I will be posting the cracked HX stories tomorrow.

Take a look at these oil photos and see if you can guess what the ambient CO was.

Mark H

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