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  1. #1
    Join Date
    Mar 2002
    Posts
    93

    Question

    In our market there are not very many techs using comb. analyzers, is it a tool that is nessisary? how does it calculate efficiency on a gas furnace?

  2. #2
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    I just ordered a new one. In todays market and the fact coustomers are smarter and more concerned about the efficiency of thier unit it has become a nessary tool

  3. #3
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    I would consider it a necessary tool.

    The efficiency calculations from a analyzer should be ignored, the only efficiency we should be concerned with is thermal efficiency.
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  4. #4
    Join Date
    Mar 2002
    Posts
    93
    Thermal efficiency? explain. This temp rise? i know i should know this.

  5. #5
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    It's the actual BTU's being delivered from the furnace versus the rated BTU output of the furnace.

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  6. #6
    Join Date
    Mar 2002
    Posts
    93
    and an analyzer does that?

  7. #7
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    No,it doesn't.

    You can do it with a thermometer & a magnehelic.

    You need CFM & delta T to figure it based on the sensible heat formula.
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  8. #8
    Join Date
    Mar 2002
    Location
    Gaylord, Michigan
    Posts
    729
    Originally posted by davidr
    I would consider it a necessary tool.

    The efficiency calculations from a analyzer should be ignored, the only efficiency we should be concerned with is thermal efficiency.
    Is thermal efficency taking into account the total system? As in duct system?

    If so, wouldnt it be to the techs advantage to have both figures at their fingers? One to show that (possibly) the furnace is working at 90% efficency, but the customers total system is 75% efficent?

    Which in turn could lead to duct renovations. Or am I totally off base here?

  9. #9
    Join Date
    Aug 2003
    Location
    Central Kentucky
    Posts
    6,248
    Originally posted by Christheheatingdude


    Is thermal efficency taking into account the total system? As in duct system?

    If so, wouldnt it be to the techs advantage to have both figures at their fingers? One to show that (possibly) the furnace is working at 90% efficency, but the customers total system is 75% efficent?

    Which in turn could lead to duct renovations. Or am I totally off base here?
    The duct system should be included in the true thermal efficiency of any system,unfortunately most contractors don't have the tools to make these measurements.

    We check the efficiency of the equipment & the duct system it is the only way to verify actual BTU delivery is being accomplished.

    I would say no you are not off base, you have a very real grasp of things.

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  10. #10
    Join Date
    Oct 2005
    Posts
    69
    Keep in mind there are two different efficiencies in a furnace or any combustion device. The combustion analizers tell you your gas air ratio and tells you that you have a clean burning flame. You can adjust your gas pressure to maximize efficiency but most manufactures call for 3.5"wc. to test the efficiency of the furnace you clock the gas meter with in and out temps. A 60% efficient furnace can have a very efficient burn ratio but it's still a very inefficient furnace is it not.

  11. #11
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,478
    Since the gas industry has stated that the BTU's of natural gas will not be consistant this year it would be impossible to set a furnace correctly by measuring gas pressure or clocking a meter. 3-1/2" only works in a perfect world. Gas BTU's vary all over the country and one gas pressure does not address all the differences. A combustion analyzer is the only way to set up a furnace correctly by measuring Oxygen, Stack Temperature and CO. Then the Delta T needs to be checked along with airflow to determine how many BTU's are actually being transferred to the plenum from the fuel. With the high cost of fuel this year people will be looking for savings and this cannot be accomplished without a combustion analyzer and the necessary training on how to use it.
    captain CO

  12. #12
    Join Date
    Oct 2005
    Posts
    69
    Doe not the gas valve automatically compensate for a fluctuation in gas pressure. It never hurts to have good equipment to do the best job for your customer as you can. But does the meter actually tell you what is being transferred to the heat exchanger or what is capable of being transferred to the heat exchanger. A oxy/acetylene torch at 5000 degrees can easily cut thru half inch steel but can't cut thru a .005 piece of rust. All the tools of the trade make for a better more efficient job. Do not all the new furnaces have inshot burners that are non adjustable? Even the ribbon burners are not adjustable anymore.

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