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CO True Or Not

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At what point do you call BS?? Performing a CO test at the exhaust port on a power vented furnace and had a reading of 186PPM "new furnace". HVAC tech called me and asked where I took the reading. (I took readinag at the exhaust) I explained that I do not drill/test into pvc vent pipes. He told me that he took a reading in the flue gas and his reading were 26PPM. I allowed 10 min of operation (steady state). My question is 2/9 fold:

1 If the tech did not allow for steady state would the CO level rise?

2 If I take the reading at the exhaust and that reading is significantly higher should there be a concern that the exhaust fan or pressure switch is holding back gasses.

3 If the tech adjusted the gas pressure flow before testing for CO would that decrease co level

4 The tech called me and asked where I tested ......why would he care....he is the expert right...

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I think the tech should ask you where you tested. Logical question

What was your purpose for testing? Checking the operation of the furnace? Checking the efficiency of furnace?

I suspect most inspectors are not performing that task and the hvac tech was just checking what and why you did.

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I remember when I first "discovered" CO testing. It was back in the Draeger tube days. After performing approximately 800 Draeger tests (that's back when a single pack of 10 tubes was about $50), I graduated to a Monoxor, then a Fyrite Pro.

After a few thousand more "tests", I've determined CO "testing" is nearly pointless for more reasons than I care to enumerate.

If you find a number you don't like, and you really feel it's important and critical, tell the customer to find a tech to check the furnace. If the tech says it's OK, then accept his numbers.

I try not to second guess the guy that works on equipment every day. Yes, I may know more than him, but maybe not.

And lately, I'm pretty sure not.

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Actually a CO test is beneficial, and part of the drill, when you're dialing in a gun style burner however that's a service related issue.

I've never used my CO meter to check a typical residential furnace on an inspection.

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I agree,

I did a first year inspection on a house a week ago for a fellow who'd used another inspector for his initial inspection. The other guy had taken C.O. readings and reported them as high but that's it.

The installer had configured the exhaust vent with a total of four 90° bends in it, just above where it left the collar of the furnace, so that the filter could be removed from its holder. The other inspector didn't say a word about the four 90° bends.(???)

The kicker is that the back of the return air plenum above the furnace was accessible; and if they'd turned the holder 180° and placed the door on the opposite side the filter would have still been accessible and they could have taken the exhaust vent straight up through the building and roof.

I wrote up the four 90° bends and suggested to the client that he point out to the builder that if the HVAC tech flips the the holder a straight vent can be used. The client wanted me to include the other guy's C.O. reading in the report - I told him I wasn't going to record readings taken by someone else in my report, and I sure as hell didn't need to take any readings to see that the vent configuration was wrong and needed to be straightened out.

I think that some inspectors rely on their gadgets too much and not enough on their training and common sense. This causes them to end up in situations where they can't see the forest for the trees.

ONE TEAM - ONE FIGHT!!!

Mike

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I agree with Kurt and Mike regarding the benefits of CO testing during a home inspection. But . . . .

According to the Building Performance Institute (www.bpi.org) guidelines:

You should definitely be at steady state, and I would think 10 minutes is plenty. But I think this allows the CO level to drop, not rise.

You were right not to drill through a power vented flue, and to measure at the exterior outlet. I hope the tech recognizes this.

CO levels should be below 25 ppm, and in no case should it be above 100 ppm in undiluted flue gas.

As to why you and the tech got such different readings: there are probably a million possibilities and that's one reason why testing for CO might be futile. Way too many false positives and false negatives.

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CO levels should be below 25 ppm, and in no case should it be above 100 ppm in undiluted flue gas.

The consequences of high CO concentrations in the flue of a residential appliance being what? If you don't mind educating me.

Marc

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As to why you and the tech got such different readings: there are probably a million possibilities and that's one reason why testing for CO might be futile. Way too many false positives and false negatives.

Yep.

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CO levels should be below 25 ppm, and in no case should it be above 100 ppm in undiluted flue gas.

The consequences of high CO concentrations in the flue of a residential appliance being what? If you don't mind educating me.

Marc

I didn't write the BPI standards, of course, so don't hold me to any of this. For sealed combustion appliances I believe that it's just an efficiency issue. For atmospherically vented appliances spillage is a huge concern, and worst-case depressurization testing is also required.

If you were to argue against raising much fuss over an elevated reading in a direct vent furnace you would have a lot of company, from what I can tell. But that's what the standards say.

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