Page 1 of 4 1234 LastLast
Results 1 to 13 of 49
  1. #1

    Question TPI-708 Combustion Analyzer (questions about readings)

    1st off Hi all!

    I just got home and went to my PC to look online for some answers about the readings I have just gotten off an Armstrong 90+ 2-stage furnace. I then saw this forum after I googled and thought I'd see what you all might be able to help with, as far as some answers.

    Here's what happened...
    The local energy company was on this job and did a CO reading from the outside 2" PVC outlet vent. And then told the customer that the CO was higher on this furnace than it was on any other he had done that to (why he is doing this I don't know but I can only assume it's to make it look like he's doing something and might justify the bill he gives the customer). So after hearing the phrase "High Carbon Monoxide" the customer flipped and called us (the one's who installed it). Keep in mind this is only outside off the venting that he gets "high" carbon monoxide readings.

    I am new to the business I work for. But I have been doing heating/cooling for the last 5 years. My employer had purchased a TPI-708 Combustion Analyzer, basically it's an efficiency tester and CO/Temp reader. Hopefully a few of you here have used them or are familiar with them as I am new to them. Since I'm new to this tool, I decided to test a couple of the 90+ furnaces that my employer has heating the shop and offices, as to get an idea of what to expect on readings. I also did test out another furnace as part of a clean & check. I figured the more furnaces I test with this thing the better so I can gauge the readings and to do a compare and contrast between them all. Plus to see if this thing was worth the money or if it was a waste of time and money. And also whether or not this last job (the one that the energy company said was high CO is "normal" or if something else is going on.

    Below are the readings I got from it and what furnace it was on.

    #1
    Armstrong 90+ single stage: Nat Gas

    O - 12.4%
    XAir - 145%
    eff. - 98.1% (?) seems too high eff. reading imo.
    CO - 1ppm
    CO - 4.8%
    ch1 - 99F
    ch2 - 56F
    -CF- CO - 2ppm

    #2 Rheem Classic 90+: LPG

    O - 13.6%
    XAir - 186%
    eff. - 91%
    CO - 3ppm
    CO - 4.8%
    ch1 - 96F
    ch2 - 62F
    -CF- CO - 2ppm

    #3 Armstrong 90+ single stage: LPG

    O - 11.1%
    XAir - 113%
    eff. - 91.4%
    CO - 2ppm
    CO - 6.4%
    ch1 - 98F
    ch2 - 58F
    -CF- CO - 4ppm

    OK now the "high CO" furnace which as you will see is higher/different than the rest.

    #4 Armstrong 90+ two stage: Nat Gas

    1st stage readings:
    O - 9.0%
    XAir - 75%
    eff. - 88.8%
    CO - 1ppm
    CO - 6.7%
    ch1 - 87F
    ch2 - 51F
    -CF- CO - 1ppm

    2nd stage readings:
    O - 5.8%
    XAir - 38%
    eff. - 89.1%
    CO - 221ppm
    CO - 8.5%
    ch1 - 90F
    ch2 - 50F
    -CF- CO - 306ppm

    ***Note*** CO reading climbed up to 1719ppm before leveling out at 221ppm in 2nd stage. 1st stage it leveled out at 1ppm. Also all the readings are in "Gross" not "Net"

    Anyone that can tell me some "average" type readings people have gotten off this unit would be much appreciated. I have up to this point assumed the 1st 3 readings on the 3 different furnaces have been accurate. And that possibly the last Armstrong furnace has a Fuel to Air ratio problem either in the venting (which I took a look at) or the inducer motor. But there is no sign of sooting, misfiring or harsh ignition.

    Any help given is greatly appreciated.

    P.S. I checked the incomming gas pressure on both stages U-Tubed at 6" inlet and 1.9" on 1st stage and 3.5" on 2nd stage.

    [Edited by magnehelic on 01-11-2006 at 10:16 PM]

  2. #2
    The O2 reading is low and where did your X-air go. I would start checking to see if the right orfices are installed. pull the burner box door off to see if x-air increased to let you know if you have restricked intake air

  3. #3
    Join Date
    Oct 2005
    Location
    Omaha, NE
    Posts
    309

    Maybe normal but

    1. maybe normal for Armstrong. Check the spec from the mfg you can get one from Armstrong.

    or...

    2. 2nd-stage uses more Oxygen and there may not be adequate O2 to burn, therefore CO production. CO is produced when Fuel/Air ratio is high (there is more fuel than O2 available). I assume combustion air is inadequate:
    - ? Intake port has debris: small animals like birds etc.; or small leaves sucked inside during the fautumn.

    - To see if more air decreases CO level, open the side port (inside the furnace, close to the combustion chamber, there should be a plastic cap on the intake piping, to allow air in the vicinity of the furnace to bypass and enter the combustion chmaber), then re-measure the gases.

    Note CO2 is carbon DIOXIDE; CO is carbon MONOXIDE (CO is the gas that killed the 12 miners in W. VA recently).


  4. #4
    Join Date
    May 2001
    Location
    Kansas City
    Posts
    2,729
    Where are you checking at? Don't check a draft induced furnace at the flue outlet, drill a hole just above the furnace outlet. Your O2 and excess air is too high on the shop furnaces, did you check the gas pressure on them?
    On the furnace in question did the CO level jump when the blower came on? That would indicate infiltration of air into the heat exchanger from a hole or crack. Also if its 2 piped pull off the intake and see if it makes a difference.
    Here's a lot of good info. http://www.bacharach-training.com/
    Take a class if you get a chance.

  5. #5

    Re: Maybe normal but

    Originally posted by cn
    1. maybe normal for Armstrong. Check the spec from the mfg you can get one from Armstrong.

    Note CO2 is carbon DIOXIDE; CO is carbon MONOXIDE (CO is the gas that killed the 12 miners in W. VA recently).

    Ya, my mistake by-product of working late and typing somewhat fast. I got them mixed up I see. And yes I'm calling Armstrong in the morning to get some specs on this furnace.

    Originally posted by rsmith46
    Where are you checking at? Don't check a draft induced furnace at the flue outlet, drill a hole just above the furnace outlet. http://www.bacharach-training.com/
    Take a class if you get a chance.
    I am drilling holes, I did take a quick class put on by a local distributor, but it ended up being more of a sales pitch for TPI's other equipment. Thanks for the link too, I got it bookmarked!

    P.S. thanks for the quick replies so far. You all seem to be pointing toward comb. air as the next thing to check thoroughly. Which I was pointing at in ways to myself on the job, but was unsure of the tool and what to expect from a 2 stage or any furnace for that matter. And not being familiar with this I wanted to run it past some people who actually have used it in the field. (I wished it had been earlier in the day so I could have spent the extra time diagnosing the full venting as it was I cut the exhaust vent and checked it. Just not the intake.)

    I'm starting to feel more comfortable with this TPI-708 if you all seem to agree that the 1st 3 furnace readings are "normal"? so to speak.

    [Edited by magnehelic on 01-12-2006 at 12:58 AM]

  6. #6
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    Originally posted by rsmith46
    Where are you checking at? Don't check a draft induced furnace at the flue outlet, drill a hole just above the furnace outlet. Your O2 and excess air is too high on the shop furnaces, did you check the gas pressure on them?
    On the furnace in question did the CO level jump when the blower came on? That would indicate infiltration of air into the heat exchanger from a hole or crack. Also if its 2 piped pull off the intake and see if it makes a difference.
    Here's a lot of good info. http://www.bacharach-training.com/
    Take a class if you get a chance.
    This is great advice make sure that your test hole is about 12" to 18" away from the inducer outlet though.

    From the readings you gave it looks as though the first 3 furnaces might be underfired. I am assuming the ch1 & ch2 readings supply & return air temperatures?

    Before you get to comfortable with combustion testing I would also highly recommend some training also.
    Another link you can check out in addition to Bacharachs is http://www.nationalcomfortinstitute.com.
    The two guys you need to get in touch with for training are Jim Davis with the National Comfort Institute & Rudy Leatherman with Bacharach. These guys are tops in my book when it comes to providing you with the information required to do proper combustion diagnostics.

    Good Luck with your testing!
    Have you set up a Google alert for Carbon Monoxide yet?
    Click here to find out how.

  7. #7
    Join Date
    Feb 2004
    Location
    southern illinois
    Posts
    5,536
    i was told at meeting last spring to not drill pvc pipe as it is hard to seal up and readings at vent termination would be sufficent,....also how would you do a mobile home furnace without taking readings at vent termination?

  8. #8
    Join Date
    May 2001
    Location
    Kansas City
    Posts
    2,729
    Agree that first three furnace readings are not normal, O2 & excess air are high indicating underfired. That's why I asked if you checked the gas pressure.
    The last furnace looks normal on low fire but on high fire the O2 level is low & CO is high. Lack of combustion air is most likely. When you don't have enough excess air one of the Oxygen molecules in the CO2 is burned leaving high CO level.

  9. #9
    Join Date
    Dec 2005
    Posts
    94
    When you checked the gas pressure did you remove the air pressure tube from the burner box to the gas valve. If you didn't know, it is there to compensate for the fact that the pressure in the burner box is lower than the atmospheric and that is what the top of the diaphragm needs to see to deliver the proper pressure in the burner box. Adjusting gas pressure with the tube on will result in the wrong input. Anyway you are being very thorough. Just thought I'd throw that it.

  10. #10
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,538

    Combustion readings

    The first three furnaces are operating less than 60% efficiency and the Rheem is probably less than 50%.
    The 2-Stage Armstrong is the only one operating anywhere close to proper but it is slightly overfired in High-Fire. The gas pressure needs to be backed off slightly.

    Ideal Oxygen readings would be 6%-9%, with 6% being the best. The flue temperature in High-Fire should be 120-140 degrees.

    Anytime Oxygen is above 9% the flame temperature at the burner is extremely low and the amount of BTU's that are actually being produced by the fuel that are usable are reduced 20-30%. The low flame temperature creates a low flue temperature which then are calculated into false high efficiencies.
    6% O2 = 2800 degree flame
    9% O2 = 2300 degree flame
    11% O2 = 1900 degree flame
    13% O2 = 1600 degree flame
    Which of the flame above do you think will deliver the most heat??
    captain CO

  11. #11
    Join Date
    Dec 2005
    Posts
    94
    For Jim Davis
    you sound pretty knowledgeable about this so maybe you can clear up something for me. I've done startups on larger commercial waterheaters, boilers and furnaces, as well as clean and checks on oil furnaces using combustion analysis for burner setup. The 6-9% O2 readings you quote pretty standard. But when I analyze condensing furnaces like magahelic is talking about, they are always much closer to the readings he gets on the first few clean running(no CO) furnaces. I was wondering if that is due to the fact that we are condensing down the H2O from a vapor and therefore changing the other percentages in the mix.

  12. #12
    Join Date
    Sep 2004
    Location
    Glendale AZ
    Posts
    299
    edit
    The bitterness of poor quality remains long after the sweetness of low price has gone.

  13. #13
    Join Date
    Aug 2005
    Posts
    833

    Re: Combustion readings

    Originally posted by Jim Davis
    The first three furnaces are operating less than 60% efficiency and the Rheem is probably less than 50%.
    The 2-Stage Armstrong is the only one operating anywhere close to proper but it is slightly overfired in High-Fire. The gas pressure needs to be backed off slightly.

    Ideal Oxygen readings would be 6%-9%, with 6% being the best. The flue temperature in High-Fire should be 120-140 degrees.

    Anytime Oxygen is above 9% the flame temperature at the burner is extremely low and the amount of BTU's that are actually being produced by the fuel that are usable are reduced 20-30%. The low flame temperature creates a low flue temperature which then are calculated into false high efficiencies.
    6% O2 = 2800 degree flame
    9% O2 = 2300 degree flame
    11% O2 = 1900 degree flame
    13% O2 = 1600 degree flame
    Which of the flame above do you think will deliver the most heat??
    Re: false efficiencies, cant you get bacharach to do something about how they calculate efficiency on their testers so I dont have to constantly explain to customers that the efficiency number that I just lowered by increasing stack temperature really doesn't mean anything?

    Re: Two stage Armstrong: should they disable the low stage?

    eventu rerum stolidi didicere magistro

Page 1 of 4 1234 LastLast

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event