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Testing gas fired equiptment question

clammy Member Posts: 2,829
I have a question on the proper location for flue gas sampling in gas fired boiler when the flue divertor is built into the boiler (peerless,utia ,buderus and others) Should the flue colletor above the sections be drill and tested from there or is it ok to take your sample from above the built in divertor .I am more familar with oil fired equiptment and mod cons testing formats.MY main corcern is that take a smaple above the collector will show a reading of exess air due to dilation and mixing of room air thanks peace and good luck clammy
R.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating


  • Tim McElwain
    Tim McElwain Member Posts: 4,556
    Testing should be

    done before the draft hood in all cases. It is sometimes difficult but with a little effort it can be done. We will be covering this extensively in our class on testing starting this coming Monday.

    With water heaters I drill a hole at an angle into the draft hood so as get down into the flue passage of the heater.

    I do however measure draft both before and after the draft hood to insure not being affected by "curtain effect" (excessive draft after the draft hood with no draft before the hood).

    Warm air furnaces should have each section given a combustion test and then averaged out after all measurements. This again is often with some difficulty due to draft hood being built in to the unit.

    On Mod/Con equipment if not test points are given you can drill a hole in the vent 18" to 24" away from the point of exit on the equipment. Just reseal the hole with high temp sealant of tap and install a stainless steel bolt.
  • Steamhead
    Steamhead Member Posts: 15,767
    If the probe on your analyzer is long enough

    as on my Testo units, it can reach into the flue collector past the draft hood area and sample the flue gases from right above the sections. They are not diluted at this point.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • clammy
    clammy Member Posts: 2,829
    Thanks gentlemen

    Thanks Tim and Frank the probe on my e instrument anaylizer  really is not that long and on some gas boilers a bit tough ,my thinking was  to drill (and later seal hi temp rtv) into either the side or top of the flue colletor for testing purposes .Does any one see a promblem with this pratice?Besides trying to get a good reading between the 3 or 4 boiler setion for a good average reading ?thanks again peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
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