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Old 11-11-2011, 06:11 PM   #1
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CO levels from ductwork...what is acceptable?


Hello,

I have a Lennox Pulse G14 gas furnace that was installed in 1988, that was also part of a recall campaign in the late 90's. My furnace did have a cracked heat exchanger, and it was replaced under warranty in 1999.

I had a new heating contractor come to my house today to clean my furnace, and as soon as he saw the model he said I might have a cracked heat exchanger. I explained that it was replaced 12 years ago and I doubted there was a problem since my CO detectors never go off, so he gets a CO monitor from his truck and places it on a heating vent and fires up the furnace.

After 5 minutes the reading from the heat register was 8 PPM, and after 20 minutes it had gone up to 20 PPM but did not rise any further. He advised he suspected the heat exchanger was faulty, and proceeded to quote me on a new furnace.

He did explain that a pressure test of the heat exchanger would prove beyond doubt if this was the issue and offerred to do that, but I got called into work and had to leave so we didn't have time to do a pressure test.

I'm just looking for some advice here as I want to make sure this isn't normal or "acceptable" before spending $3000 on a new furnace. My gut tells me that there should be no CO coming from the ducts at all, but I've read on some other websites that some furnaces will spill CO during startup so I want to make sure there really is a problem here.

Should I pay him to come back and do the pressure test just to be sure? Even though the heat exchanger is 12 years old the rest of the unit is 23 years old and can't last forever....but having said that it has never quit or needed any repair work other than the heat exchanger, so need some advice.

Thanks

Michael
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Old 11-11-2011, 06:25 PM   #2
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CO levels from ductwork...what is acceptable?


Google : allowable co levels

http://www.carbon-monoxide-poisoning...co-levels.html
http://www.osha.gov/SLTC/healthguide...cognition.html
http://www.epa.gov/iaq/co.html

There should be NO CO levels. I know that furnace like the back of my hand and installed hundreds of them. Unfortunately some of the parts are obsolete as the suppliers who made them for Lennox have gone broke etc. I just replaced the 26 yr old one I had in Mom's house for that reason. It will start to develop intermittent problems and nickel and dime you to death.
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Last edited by yuri; 11-11-2011 at 07:06 PM.
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Old 11-11-2011, 06:31 PM   #3
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CO levels from ductwork...what is acceptable?


Seems like your choice is die or pay this guy three kilobucks.

But, from
http://www.cpsc.gov/cpscpub/pubs/466.html

"On average, about 170 people in the United States die every year from CO produced by non-automotive consumer products."

so this hazard is about 3x more likely than a lightning strike and way safer than driving a car.

For this much money get an independent opinion, perhaps from a forensic consultant who does not sell furnaces or furnace parts.


Or you could ask your tech to fill out a sworn statement as to his results and his interpretation of the danger. Even politicians avoid going under oath.
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Old 11-11-2011, 06:33 PM   #4
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CO levels from ductwork...what is acceptable?


Momentary spillage from a start up ignition does not apply to a pulse.
There is no reason to have those measurements in your heating duct except from an exhanger crack!
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Old 11-11-2011, 06:35 PM   #5
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CO levels from ductwork...what is acceptable?


Pressure test is the only acceptable heat exchanger test on a pulse. Co in the air stream is not a reliable indication of a heat exchanger leak. Co can be brought in from leaking returns and a water heater flue spilling.

Just saw yuri's 15 year warranty on the replacement exchanger. I did not know that.

Last edited by Marty S.; 11-11-2011 at 06:38 PM.
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Old 11-11-2011, 06:57 PM   #6
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CO levels from ductwork...what is acceptable?


Pressure test it.
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Old 11-11-2011, 06:57 PM   #7
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CO levels from ductwork...what is acceptable?


A few years ago I had a older client who was in the process of finding a rest home for his wife who was acting erratically. Yeah, you quessed it.
A loose chimney vent from a HW tank. He was an avid golfer and spent much of his time outside and so felt few of the effects where as she was the homebody slowly accumulating the co. He called me back a month later after the fix to say that she was back to normal and to please not mention his rest home plans for her on my next visit.

Your right Marty S it might be from something else but what ever the source, that level of co in a heating duct needs to be addressed!

Last edited by how; 11-11-2011 at 07:03 PM.
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Old 11-11-2011, 07:23 PM   #8
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CO levels from ductwork...what is acceptable?


Quote:
Originally Posted by Marty S. View Post
Pressure test is the only acceptable heat exchanger test on a pulse. Co in the air stream is not a reliable indication of a heat exchanger leak. Co can be brought in from leaking returns and a water heater flue spilling.
The only gas burning appliance is this furnace, so if this is not a normal condition it must be coming from the furnace somehow.

I am not adverse to spending the money for a new unit, but just want some piece of mind that I'm not getting sucked into a sale based on a CO reading caused by something else that is a simple fix.

I have been burned by contractors before and just wanted a second opinion.

Thanks

Michael
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Old 11-11-2011, 07:50 PM   #9
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CO levels from ductwork...what is acceptable?


Quote:
Originally Posted by mrennie View Post
The only gas burning appliance is this furnace, so if this is not a normal condition it must be coming from the furnace somehow.

I am not adverse to spending the money for a new unit, but just want some piece of mind that I'm not getting sucked into a sale based on a CO reading caused by something else that is a simple fix.

I have been burned by contractors before and just wanted a second opinion.

Thanks

Michael
easy solution get a second opinion
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Old 11-12-2011, 03:29 AM   #10
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CO levels from ductwork...what is acceptable?


Co can come from a gas clothes drier, gas water heater, gas range, and from your garage(if a car was ran in it in the last hour or so before the test,). Pressure test the furnace.
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Old 11-12-2011, 07:28 AM   #11
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CO levels from ductwork...what is acceptable?


Quote:
Originally Posted by carmon View Post
easy solution get a second opinion
Unfortunately, not so easy where I live. Population 5000 people and only 2 HVAC contractors. The other contractor (not the one that came yesterday) is the one that did the heat exchanger relacement in 1999 and due to their unreliability and poor service I refuse to use them. (The day they changed the heat exchanger back in 1999, the left without confirming the furnace was working. I called the trouble in at 4PM and when the owner of the company finally came back at 11PM he was so drunk I had to help him down my stairs into the basement!)

I'll get the new contractor back to pressure test it, although my wife is suddenly keen to get rid of the Brrrrrrrr sound of the Pulse furnace so might go ahead regardless.

Thanks
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Old 11-12-2011, 08:25 PM   #12
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CO levels from ductwork...what is acceptable?


problem again with heat exchanger ,,,,I would look for other problems seem odd to only get 10-11 yrs from new exchanger........
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Old 11-13-2011, 05:25 PM   #13
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CO levels from ductwork...what is acceptable?


When professional CO meters fail, are they more likely to fail by reading high? For safety reasons this outcome is better than if they fail by reading low.

What percent of HVAC firms actually observe the manufacturer's recommend calibration interval?
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Old 11-13-2011, 05:48 PM   #14
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CO levels from ductwork...what is acceptable?


They give erratic readings.
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Old 11-13-2011, 06:02 PM   #15
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CO levels from ductwork...what is acceptable?


My C75 UEI co detecter yearly calibration is $150.00 with an extra $200.00 every other year or more extensive servicing. I've never been happy with some of the readings since it often measures higher than possible efficiency readings on older units. My meter is 5 years old and coming up on another $350.00 type of service, so I'm wondering about switching brands and what other gas tech's experiences and unit preferences are.
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