I need Charlie or David on this one.

So I was doing a new construction 11 month inspection today. I decided to do a combustion test on the package unit because they had blocked the access panel with a retaining wall. I let the unit run for 5 minutes and proceeded with the test. I got 1004 ppm at steady state! Now with RESNET standards I’m supposed to call in an HVAC tech when I exceed just 100 ppm. Any advice on what’s causing this? The fresh air intakes were not restricted due to the wall.

Will I am not understanding Your combustion Test has to do with the burners as with the mixture of air to gas ratio. A carbon monoxide test has to do with the amount or carbon monoxide in the discharge air stream (supply air) as in a cracked heat exchanger where combustion air enters the supply air. Which one were you testing combustion air or supply air

Combustion. I realize the system needs to be tuned but I’m trying to get a better understanding of the whole process. I had to undergo “combustion training” through RESNET, and I thought the training was total crap if you ask me. The basic pass or fail combustion test they want us to call out is if a unit produces more than 100 ppm then it fails testing and the protocol is to call in a HVAC tech to either fix or replace the unit. That’s about all they gave us for information. I also tested at the supplies and there was no cracked heat exchanger, but of course they don’t tell us to check this, which I find extremely odd.

Would you consider this a failed combustion test with your knowledge? And what would you recommend?

Will a combustion test is not a all inclusive PPM test its a measurement of stack temp, % of oxygen it basically tells you what % of your fuel is being burnt and what is going up the stack unburnt. I think you are confusing a combustion test with a carbon monoxide test which is measured in PPM

Tell me where you are taking your PPM sample from and then I can help you.

It’s at the flue. I’m trying to upload a photo of my Testo 320’s screen, I’m not sure if it will go through (never uploaded a pic). I’m asking the question because I was asking the trainer in the RESNET training course and I really didn’t get an answer. I wanted to know the reason behind why we would fail a combustion test due to the CO ppm being above 100; he just couldn’t tell me. All they kept saying is that it was the new RESNET standard. I am aware that incomplete combustion can cause moisture and damage the equipment but why do they set the pass/fail at 100ppm? There is so much more to that test than just the CO output, so I’m trying to get a better understanding of the “standards” or why I would fail a system due to this. I do understand that a properly installed new system can actually produce 0 ppm CO.

I just ordered some new books that will help me, but I appreciate your feedback greatly.

Oh yeah if anyone besides Charlie or David knows you can answer too; I would appreciate all feedback. :mrgreen:

Too little, too late. -(

Will pay no attention to Jonas he is just being a dick head as usual. The little boy got his feelings hurt

I still think your communication between the Resnet instructor and you are missing the ball game. You appear to be testing stack (flue gas CO) which by nature is going to be in the range you are testing at. The resnet instructor is giving you PPM that the supply air side of the furnace should not exceed.

Yep i think Charlie nailed on the head . lol was there any doubt

This may help

No they are saying if the flue gas CO ppm exceeds 100 then it’s a failing test. If the supply side even started to climb on a CO test I would be suspect that the heat exchanger was cracked, and if the supply air put out 100 ppm then the occupants would be poisoned or dead. Wilson thanks for the link. I know the RESNET Standards all too well, that link is dated 2010. Resnet changes things all the time so that might be out of spec. I did find some good information on Trutechtools.com today. I basically want to understand the test much better than being trained to just look at the CO output; there is a lot more to it. From the short amount of time I read today during lunch; There are many protocols that allow up to 400 ppm and the system can be out of whack for a number of reasons.

Will it is impossible to have flue gas CO that does not read above 100 PPM

If I have not been operating a open flame appliance within the home when I test for CO on a furnace supply air I personally call out anything above 00.3 to have the furnace checked. I don’t mess around with CO

That’s what I originally thought too, but that’s not correct. A system set up right can produce 0 ppm CO. I didn’t know that until I went to training and was field testing a unit that produced 0 CO ppm, I asked the instructor if that was a correct reading and he said that if the unit was properly tuned you’ll see that most of the time on new systems.

Here is a link to the combustion literature you can get for free at truetechtools. I haven’t read all through it but from what I have read it’s some good literature. https://www.trutechtools.com/CombustionGuide

I attached an image of a flue gas analysis I did on a water heater at the same home.