Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

combustion testing

appliance. since its a double wall exhaust assembly where is the probe inserted? would i drill a hole in the cap outside?


  • Mark A. Custis
    Mark A. Custis Member Posts: 247
    Testing a direct vented

    appliance can require some doing. If the burners are open test above the flame. You might just need to drill that hole in the vent to get your probe in a good location to test the flue gasses before they get diluted. I have been know to drill an access hole in PVC venting then tap and plug the hole with a stainless steel or brass machine screw and a little 736.


    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
  • chris smith_2
    chris smith_2 Member Posts: 37
    direct vent

    alot of manufacterurs buderus and thermo dynamics want you to test thru a test port or observatin hole they provide that is right over the fire [ or kinda behind it really ] i like to also add a test hole in an elbow if there is one availible or as a last resort in the spiral duct that connects the boiler to the termination piece, i have found sometimes testing over fire does not give you the whole story, nice to have over fire and "chimney" draft and smoke measurements, when i'm done testing i plug the hole with red high temp rtv silicone this is easy to remove the next year when you go back to service the furnace/boiler hope this helps

    chris smith

    paradice porter maine
  • Rudy
    Rudy Member Posts: 482
    Testing concentric flues

    Probably the best way would be to drill a hole in the cap and take the sample there.

    I've also drilled concentric flues and sealed the holes with a lag bolt long enough to thread through both the inner and outer holes with a dab of high temp rtv to keep it in place.
  • Jim Davis
    Jim Davis Member Posts: 305

    Never test near the flame of any appliance unless it is an open flame like a gas log or top burner of a stove
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    This problem also came up on

    Oil Tech Talk and it amazes me how few know there is an adapter for this purpose.

    From what I'm finding out it does have an additional cost and so the installers are not buying them.

    On oil in MA I'm currently teaching Fire Inspectors to not issue the permit and demand that they be put in.

    It's too bad the gas inspectors are not cracking down on this, it's not only an energy issue, but one heck of a safety issue too!
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    I completely disagree,

    if we had more 'over the fire' testing and compared it to breech readings a lot more air leaks and hazardous conditions could be found.

    If you're talking directly into the fire I agree and my apologies.

    But, if you're talking over the fire, you better do some reading because that has been an accepted way since the 1920's and I can send you a page from a text of that era to prove it, FACT!
  • heatboy
    heatboy Member Posts: 1,468
    Wouldn't you think........

    that the manufacturer would give you a test tap(s) so we could actually do the testing without doing something as dumb as drilling a hole in a positive pressure vent. Maybe their equipment is so good, combustion testing is never required ;-)


    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"

    The Radiant Whisperer

    "The laws of physics will outweigh the laws of ecomomics every time."
  • Had an

    interesting talk w/ a rep from one of the largest vent manufacturers in our area. Asked him how we should test w/ his B & L Vents. He said, "drill a hole." I said,"how do we seal it?" He answered, "good question." He did add that his company is in the process of designing an adapter for testing. What's that about the cart before the horse?

    And yes, Jim. Overfire testing, where possible, should be a fact of life on combustion equipment. Better 2 pictures than 1. Particularly with direct vent.
  • Jim Davis
    Jim Davis Member Posts: 305
    Testing over the fire?

    When testing in the outlet of a heat exchanger it may take 3, 6, 9, sets of readings before the proper location for testing is even established. Testing over the flame would require a test every 1/4" of the flame and all readings would be different. In the 1920's they did not have continuous sampling analyzers. They also recommended adjusting by flame color. Neither method of testing or evaluation in the 20's was even close, but it was the best they could do.
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    C' mon Jim gimme a break will ya!

    All you talk about is electronics. You sound like a broken record!

    I have them all, Lynn, Testo, Bacharach, Kane-May, Beckett, you name it. Know what I teach the most, wet-kits. Know why?
    It's the most used out there, FACT!

    How can you say that doing a CO@ or O2 if you wish is not important. How do you determine if there are air leaks through the heat exchanger?
    If you take an over-fire CO2 and compare it to a breeching CO2 you can learn an awful lot about burner performance and other important things.

    And as far as location, that's been prescribed even by the DOE as in the breeching and has been for twenty years.
  • Jackchips
    Jackchips Member Posts: 344
    I love these

    point, counterpoint discussions. Keep it coming guys.

    Now we need to keep Timmie involved.

    Timmie, where are you?
  • Jim Davis
    Jim Davis Member Posts: 305

    The breeching is the outlet isn't it?. You can learn about as much with a wet kit CO2 test in a flame as you can with a Polaroid Camera at half-time of a football game. I teach and demonstrate that you have about a 1 in 3 chance or less of taking a correct test with a wet kit versus an electronic tester, plus you need three hands to use it.
    I threw away my record player so I would rather like to be called a broken CD.
  • Steve Ebels
    Steve Ebels Member Posts: 904
    I agree HB

    The only way I test a positive pressure appliance is at the outlet of the exhaust. If it means 20 trips up and down the stairs to check readings then that's what it takes. The problem with this is on long vents, I'm sure that the readings get messed up due to flue gas temp drop and other factors.

    I have contemplated drilling a hole in the vent but I sure wouldn't plug it with anything except a stainless steel fastener. On a concentric vented appliance, my humble opinion is that the manufacturers should be providing test ports for this purpose. It's just stupid not to. Viessmann BTW, hass test ports for both the intake and exhaust piping on the Vitodens series. Leave it to them to shine the light for the rest and lead the way.
  • Firedragon_4
    Firedragon_4 Member Posts: 1,436
    Now I can honestly say I've

    heard it all!
This discussion has been closed.