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Old 11-13-2011, 06:16 PM   #16
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CO levels from ductwork...what is acceptable?


Bacharach, tech 60. Don't worry about the efficiency they say. But the combustion numbers.

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Old 11-16-2011, 08:07 PM   #17
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CO levels from ductwork...what is acceptable?


Update.....so I called the contractor and asked him to come back and pressure test my heat exchanger. I could tell he really thought it was a waste of time, but I said I wanted it done anyway.

He came by tonight and I watched him do the test start to finish. Note that the furnace had been running for 20 minutes before he showed up if that matters.

He plugged the inlet and outlet of the heat exchanger with expandable plugs, then screwed a pipe/gauge assembly into where the gas manifold connects to the heat exchanger, and pumped it to 4 psi.

After 4 minutes the pressure had dropped to 3 psi, and it stayed at 3 psi until he finished the test after a total of 12 minutes.

I asked him what he thought of the results since he seemed so sure the pressure was going to drop like a rock, and he admitted he was surprised.

I then questioned how frequently he had his CO detector calibrated, and he really didn't answer me, but said he had a new one he just bought, so he tries it on a floor vent after putting the furnace back together, and after 10 minutes it reads 0 PPM of C.O. We let it run another 20 minutes and the highest it recorded was 8 PPM.

He still thinks my heat exchanger is cracked and I need a new furnace, but now I'm upset that the readings between his 2 meters are not even close to similar, and without being an HVAC tech I don't know if a drop of 1 psi after 12 minutes is acceptable or not.

What do you make of this?

Thanks

Michael
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Old 11-16-2011, 08:30 PM   #18
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CO levels from ductwork...what is acceptable?


Lennox states that it can lose pressure down to 1 psi in 10 minutes and still be OK. If it even holds 1 psi for 10 mins they won't give me a credit for a failed heat exchanger so you are OK. Having said that there are obsolete parts in that furnace and you may want to consider a new one. If the purge blower fails you can get raw gas buildup in the chamber and one heck of a bang when it starts. Those blowers fail and you can get other intermittent hard to troubleshoot problems with a unit that old. I replaced Mom's Pulse this Summer for that reason and I had spare parts but did not need the aggravation of looking after it anymore.
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Old 11-16-2011, 08:52 PM   #19
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CO levels from ductwork...what is acceptable?


Do you have any other gas appliances in the home that could account for the 8 ppm spillage into your home? Pressure tests are good indicaters of cracks but as a cold test procedure they don't work well in furnaces with small cracks or seams that only open up under heat firing conditions. Unless you can find an alternative source of the 8 ppm in your home that appears when the furnace fires up, then I think you have cause to change your furnace.

If you suspect someones meter is giving a false positive co reading, (which is unlikely) get them to run the meter for 10 minutes in the home when you've arranged to have the heat right off and a few doors opened to air out the house for an hour before their visit. If their meter maintains a 0 ppm in the home with the heat off for 10 minutes, then turn on the furnace to see if the meter then rises up to 8ppm.

If that 8 ppm is real then I'd want to find out where it's coming from and eliminate it.

Last edited by how; 11-16-2011 at 09:08 PM.
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Old 11-16-2011, 08:53 PM   #20
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CO levels from ductwork...what is acceptable?


Quote:
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Lennox states that it can lose pressure down to 1 psi in 10 minutes and still be OK. If it even holds 1 psi for 10 mins they won't give me a credit for a failed heat exchanger so you are OK. Having said that there are obsolete parts in that furnace and you may want to consider a new one. If the purge blower fails you can get raw gas buildup in the chamber and one heck of a bang when it starts. Those blowers fail and you can get other intermittent hard to troubleshoot problems with a unit that old. I replaced Mom's Pulse this Summer for that reason and I had spare parts but did not need the aggravation of looking after it anymore.
Hi Yuri,

Thanks for the feedback.

It sure sounds like this isn't the crisis the contractor originally made it out to be. The furnace runs fine and I had no intention of replacing it unless it crapped out on it's own or failed the pressure test, so considering it runs fine and held 3 PSI after 12 minutes I am not seeing a problem here, except that the contractors old and new CO detectors don't jive.

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Old 11-16-2011, 08:59 PM   #21
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CO levels from ductwork...what is acceptable?


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Originally Posted by how View Post
Do you have any other gas appliances in the home that could account for the 8 ppm spillage into your home? Pressure tests are good indicaters of cracks but as a cold test procedure they don't work well with small cracks or seams that only open up under heat firing conditions. Unless you can find an alternative source of the 8 ppm in your home that appears when the furnace fires up, then I think you have cause to change your furnace.

If you suspect someones meter is giving a false positive co reading, (which is unlikely)get them to run the meter for 10 minutes in the home when you've had the heat right off and a few doors opened to air out the house for an hour. If their meter has maintained a 0 ppm with the heat off, then turn on the furnace to see if it then rises to 8ppm.
I have no other gas appliances other that this unit.

The tech was not reading the levels in the open, he is putting the meter directly on the heat register if that matters.

This new meter he used read zero for quite awhile and it took 30 minutes to get to 8 PPM and no higher. My furnace had been off for 30 minutes before this while he took it apart and reassembled after the pressure test.

Note that the pressure test was performed after the furnace had already been running for 20 minutes so it was already hot, and I think this would actually have shown a worse result if there was a crack as it should have been more open as you suggest.

Last edited by mrennie; 11-16-2011 at 09:03 PM.
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Old 11-17-2011, 08:46 AM   #22
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CO levels from ductwork...what is acceptable?


It doesn't seem like you have enough probable cause to pursue this tech for fraud. Even if you did, at least in MD, virtually no one goes to jail for this. This also seems to be true in the whole of the US.

In this battle of wits, and with the tech having every advantage, I say
You - 1 point
Tech - 0
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Old 11-17-2011, 10:06 AM   #23
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CO levels from ductwork...what is acceptable?


Hey Yuri
Does Lennox have an unacceptable level of Co for a duct measurement of its pulse the way it does for it's exchanger pressure test?
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Old 11-17-2011, 12:18 PM   #24
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CO levels from ductwork...what is acceptable?


How
The answer is no. If it passed pressure test but shows co in the duct after running for a while I would replace the flame sensor and spark plug. Bet the metal around their threads is expanding with heat which lets a little co out.
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Old 11-17-2011, 06:13 PM   #25
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CO levels from ductwork...what is acceptable?


Not that I know of and NO it would be unfeasible as the concentration with vary with the amount of air movement so it could not be done scientifically and with legality.
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Old 11-17-2011, 09:44 PM   #26
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CO levels from ductwork...what is acceptable?


At this point I can't feel confident about either CO reading that the contractor's tester showed, maybe the 8 PPM isn't even true.....so I have secured a CO/noxious gas tester from another department in my company that uses them for testing manholes and confined spaces before entering them.

It is a unit that is only a few months old and the manager of that department was kind enough to lend it to me for the weekend, so tomorrow night after work I'll be doing a thorough test of my house and furnace and see what I get with this tester.

I'll report back what I find.

Thanks for the help and advice so far, I do appreciate it.

Michael

Last edited by mrennie; 11-18-2011 at 06:24 AM.
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Old 11-19-2011, 12:12 PM   #27
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CO levels from ductwork...what is acceptable?


Well I cannot find any problem at all.

I did some testing last night and let the furnance run for a full hour and could not detect any CO from the vents. The meter would occasionally go from 0 to 1 PPM for a second but never stayed at 1 PPM for any length of time. I then turned the furnace down and let it cool down and operate normally, still nothing detected through each cycle. The meter I borrowed was calibrated 2 days ago and I have no reason not to trust it.

It also came with an air pump probe, so I attached that to the meter and sniffed all around the furnace, including the cabinet, ducts, vent pipe coupings, and condensate drain.

The only place I could get a CO reading was at the top of the condensate drain pipe opening where it attaches to the vent pipe, and I got a reading of 2 PPM here. Not sure if this is because the condensate carries CO with it as it drips from the vent pipe into the drain, but regardless, I cannot get a reading anywhere in the house under normal operating conditions.

The meter seems quite sensitive. The exhaust vent for the furnace is about 4 feet from my patio door, and when I opened the door to put out my dog this morning the furnace was running and I had the tester sitting on the floor near a vent opening about 2 feet from the door, and as soon as the door was opened the meter started counting CO and jumped up to 11 PPM.

Note that the 2 times the tech tested and found CO readings the patio door had not been opened for at least 8 hours so the readings he got could not be caused by my furnace exhaust coming in through that door.

My only explanation is that his meters are junk or not calibrated properly.

I'm going to do more testing over the weekend but unless I can detect anything I'm confident there is no safety hazard.
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Old 11-19-2011, 02:29 PM   #28
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CO levels from ductwork...what is acceptable?


Next time furnace is running, place meter at that same vent and turn on your bathroom exhaust fan.
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Old 11-20-2011, 01:58 PM   #29
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CO levels from ductwork...what is acceptable?


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Next time furnace is running, place meter at that same vent and turn on your bathroom exhaust fan.
I tried that this morning and no difference, still 0 PPM on tester.

Good news is I'm not buying a new furnace!!!
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Old 11-20-2011, 02:54 PM   #30
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CO levels from ductwork...what is acceptable?


Some use Co detection as a tool just to make sells.

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