Thread: Testing for CO near the plenum

Good morning,

I’m looking for some advice. What do you guys suggest about checking for CO near the plenum of a furnace. As an inspector do you do it or not and why ?

I was told inspectors are not required to but it’s a good idea to check for co anyway.

I was also told not to do it because I would be setting myself up for trouble. I was told if you say it’s good but there was a leak now you’re liable. I was told you need to get the plenum really hot and then let it cool down to properly check for co leaks. So if you didn’t get it hot enough or let it cool down enough you could miss the leak. Is this accurate?

I do not have a co detector but I use a tiff 8800. Is this good enough for co detection?

Is it also true that you can check to see if a high efficient furnace is running right by using a co detector at the exhaust? Is this a good practice?

Thank you for your help!

Mike



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Originally Posted by Mike Krueger

Good morning,

I’m looking for some advice. What do you guys suggest about checking for CO near the plenum of a furnace. As an inspector do you do it or not and why ?

I was told inspectors are not required to but it’s a good idea to check for co anyway.

I was also told not to do it because I would be setting myself up for trouble. I was told if you say it’s good but there was a leak now you’re liable. I was told you need to get the plenum really hot and then let it cool down to properly check for co leaks. So if you didn’t get it hot enough or let it cool down enough you could miss the leak. Is this accurate?

I do not have a co detector but I use a tiff 8800. Is this good enough for co detection?

Is it also true that you can check to see if a high efficient furnace is running right by using a co detector at the exhaust? Is this a good practice?

Thank you for your help!

Mike

I do not test for CO. If I suspect that the unit might have a problem I report it as needing repairs or replacement.

If you test for CO, do you test for it at gas ovens? They produce fairly good levels of CO when they are operating properly! It's just not the turkey that makes everyone sleepy at Thanksgiving!

Any time you go above and beyond the scope of an inspection, you open the door for more issues to arise..

In my opinion, testing for CO at a high efficiency exhaust is not a good idea. Most CO detectors are sensitive to heat and moisture so you can see where this is not a good idea. A combustion analyzer is the proper tool to perform in a flue or at a PVC line (not where it exits at the exhaust).

I carry a CO detector as a form of personal protection during a home inspection. If it registers high CO during an inspection and I can identify the probable or possible source, I have something that I can include in my report. If it does not register anything, I don't mention it because I do not include "CO testing" in a home inspection..

If you state that you include CO testing, you better be prepared to spend a lot more time during the inspection conducting a proper CO test and know what you are doing.

The TIFF 8800a is a combustible gas sniffer and does not sniff CO. It will respond to over two dozen various hydrocarbons including aldehydes that may accompany CO.

You need proper training, a properly calibrated combustion analyzer and proper application. Indisriminant spot testing can provide a false sense of security or give information that may be misapplied.

Let's say you get a combustion analyzer and take some readings on a furnace. Where do you test and why? What are you looking for? What's 'acceptable' vs. an action item? What do you do if you find 'some' CO and where? When do you detect the CO? What's the difference btw 101 ppm CO air free n the stack at start up versus after 1 minute, 5 minutes? If you find 15ppm in an air duct, what does that mean? What are the conditions in the Combustion Appliance Zone? Is this 'as is' or a 'worst case' condition? If you do find some CO, what is your recommendation as a Home Inspector?

Every inspector should wear a personal CO alarm set to 35ppm. You should carry into the home a low level CO monitor. Your contract should state you will terminate your inspection and evacuate the building at 35ppm or higher or 20% of the LEL of combustible gases. Otherwise, you need to know where to draw the line on your inspections.

Bob

I used a Bacharach Monoxor III and test CO levels in the plenum and exhaust flues of the furnace. I also check other gas appliances.

A couple things about CO analyzers

• The operator must be trained in their use.
• High CO levels do not necessarily mean cracked heat exchangers.
• Start up levels will be higher than warmed up levels
• No matter what anyone says it is normal to find some CO in the exhaust of a gas appliance
• THE OPERATOR MUST BE TRAINED IN THEIR USE

Thank you Thank you Thank you!
I appreciate all your help this is good stuff!
Mike

One thing you might want to consider is what will testing for CO near or in a plenum really tell you?

Great post as always Bob!

Originally Posted by DavidR

One thing you might want to consider is what will testing for CO near or in a plenum really tell you?

Great post as always Bob!

Hi David,

I'm told if you have co above the plenum the heat exchanger is probably cracked.

I plan to take the co test section out of my report and not offer co testing.

Thank you