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  1. #27
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    Quote Originally Posted by chuckcrj View Post
    I thought you were more intelligent than this.

    You didn't post the size of that furnace but lets say its a GCVC90905 90kbtu input.

    It has #43 orifices, 4 of them. At 3.5" you have 20,111 btu per burner for a total of 80,444 btu.

    Thats IF you have the perfect 1,000 BTU per cubic foot.

    So you sold them a 90K unit that only has an 80K input. Hope you didn't cut the manual J sizing too close.

    If you put in the 70 then it actuall only has a 60,333 input.

    Edit; I went back to the OP and saw that you did install a 70k.

    This has nothing to do with combustion efficiency. You are all over the place.

  2. #28
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    MeThinks this thread will yield some interesting information if it lasts through the 'attitude' stage.

    I hope DavidR and the other CA guys get involved... should be worth the read!

    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  3. #29
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    Quote Originally Posted by seatonheating View Post
    This has nothing to do with combustion efficiency. You are all over the place.
    So your OK if your customer is only getting 50Kbtu out of his 70k furnace? I wouldn't be.

    Combustion efficiency is only half the story. Thermal efficiency is the rest of it.

    Would you agree that if we know the btu in and we measure the btu out(temp rise X delta T X 1.08) we would be able to tell what the total efficiency is?

    Please post the temp rise and CFM if you measured it. We could get a good estimate of the efficiency.

    I didn't make up any of the stuff I posted above, the info is all out there for anyone who wants to learn. It really starts to make sense when you start mesuring and testing to make sure this equipment is doing what it was rated for.

  4. #30
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    Quote Originally Posted by chuckcrj View Post
    So your OK if your customer is only getting 50Kbtu out of his 70k furnace? I wouldn't be.

    Combustion efficiency is only half the story. Thermal efficiency is the rest of it.

    Would you agree that if we know the btu in and we measure the btu out(temp rise X delta T X 1.08) we would be able to tell what the total efficiency is?

    Please post the temp rise and CFM if you measured it. We could get a good estimate of the efficiency.

    I didn't make up any of the stuff I posted above, the info is all out there for anyone who wants to learn. It really starts to make sense when you start mesuring and testing to make sure this equipment is doing what it was rated for.

    Yawn.............


    Goodman GCVC95 Heating speed tap B + (1457 CFM) rated between .1-.5 TESP. I am at .65 so let's say I am only getting 1325 CFM at best.

    My measured temp rise was 46 degrees on high stage.

    1325 CFM = X/46 x 1.08

    1325 CFM = X/49.68

    1325 CFM = 65,826/49.68

    So if you take 95% of 70K at face value then you have 66,500 output BTU's. I am getting 65,826 BTU's.

    How will the customer every get by losing that 674 BTU's? *sarcasm*.

  5. #31
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    Quote Originally Posted by seatonheating View Post
    Yawn.............


    Goodman GCVC95 Heating speed tap B + (1457 CFM) rated between .1-.5 TESP. I am at .65 so let's say I am only getting 1325 CFM at best.

    My measured temp rise was 46 degrees on high stage.

    1325 CFM = X/46 x 1.08

    1325 CFM = X/49.68

    1325 CFM = 65,826/49.68

    So if you take 95% of 70K at face value then you have 66,500 output BTU's. I am getting 65,826 BTU's.

    How will the customer every get by losing that 674 BTU's? *sarcasm*.
    Here is a link to a gas orifice capacity chart.

    http://www.hvacredu.net/gas-codes/mo...ty%20Chart.pdf

    Since you are running 3.5" manifold pressure and the factory #43 orifices you are getting 20,111 btu per burner.

    So with 3 burners you get a total of 60,333 btu input if you gas is 1,000 btu per cu. ft.

    But wait a minute, you are getting 65,826 btu! Wow that furnace is making 109% efficiency! I have to have one of those!

    How can you get more out than you put in, even if you are losing no heat out the exhaust?

  6. #32
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    Quote Originally Posted by chuckcrj View Post
    Here is a link to a gas orifice capacity chart.

    http://www.hvacredu.net/gas-codes/mo...ty%20Chart.pdf

    Since you are running 3.5" manifold pressure and the factory #43 orifices you are getting 20,111 btu per burner.

    So with 3 burners you get a total of 60,333 btu input if you gas is 1,000 btu per cu. ft.

    But wait a minute, you are getting 65,826 btu! Wow that furnace is making 109% efficiency! I have to have one of those!

    How can you get more out than you put in, even if you are losing no heat out the exhaust?

    Sure, then I'll just raise them up to 4.5 I/wc. Get real man. Save it for the technical forums.


    Doesn't matter as his heat loss is 56,594, looks like I'm fine.


    So what you are saying is that we should be changing out orifices on a brand new furnace?? Why would they mislead and be so far off in rated capacity?

  7. #33
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    Quote Originally Posted by chuckcrj View Post
    OK since you guys want to discuss it here......

    Raising manifold pressure is not the only way to follow the instructions in the owners manual which state you must correct the input btu if it is not correct. The following quotes are from the IOM of a common furnace.(Trane TUX1 single stage condensing furnace) Right after it tells you how to clock the meter is the following;







    Clocking the meter does not take into account the btu content of the gas. Using a combustion analyzer, manometer, and temp probe, is more accurate and much faster than clocking the meter. And it gets your actual input btu to the manufacturer rating on the nameplate.

    The above furnace comes with #45 burner orifices. Lets use a 100k btu unit for example that has 5 burners. If you look at an orifice chart it will tell you that you get 17,072 BTU at 3.5" per burner.

    17,072 X 5 burners gives us an input of 85,360 BTU. WAIT A MINUTE! I thought we had a 100,000 btu input furnace?? Apparently not!

    So you have a much cooler flame due to the O2 content being high, and the flame is much smaller and therefore farther away from the HX, with the result of being much less than 90% efficient! In fact doing the sensible heat calculation (delta T X CFM X 1.08) in the above furnace will often give you 60,000 to 65,000 BTU actually being delivered to the space! I have mesured it, more than once. 85kbtu in and 65kbtu out equals 76% efficiency!!

    But the AFUE sticker says 92%......

    Its not just Trane either, take a look at what size orifices the next furnace you install has and do the math.
    If it's at 76% efficiency, and the heat isn't being absorbed, then how is the flue gas below the dew point, and condensating?
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  8. #34
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    Quote Originally Posted by hvacvegas View Post
    If it's at 76% efficiency, and the heat isn't being absorbed, then how is the flue gas below the dew point, and condensating?

    Ya, something isn't jiving here.

  9. #35
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    Quote Originally Posted by seatonheating View Post
    Sure, then I'll just raise them up to 4.5 I/wc. Get real man. Save it for the technical forums.


    Doesn't matter as his heat loss is 56,594, looks like I'm fine. So the temp rise numbers it post #30 were just pulled out of thin air and not actually measured? I suspected that. In fact I knew it because it wasn't possible.
    So what you are saying is that we should be changing out orifices on a brand new furnace?? Why would they mislead and be so far off in rated capacity?
    The following is from Goodman Service Manual for the GCVC950704;

    EXAMPLE: It is found by the gas meter, that it takes forty
    (40) seconds for the hand on the cubic foot dial to make one
    complete revolution, with all appliances off, except the furnace.
    Take this information and locate it on the gas rate
    chart. Observe the forty (40) seconds, locate and read across
    to the one (1) cubic foot dial column. There we find the number
    90, which shows that ninety (90) cubic feet of gas will be
    consumed in one (1) hour.
    Let's assume the local gas utility has stated that the calorific
    value of the gas is 1,025 BTU per cubic foot.
    Multiplying the ninety (90) cubic feet by 1,025 BTU per cubic
    foot gives us an input of 92,250 BTUH.
    Checking the BTU input on the rating plate of the furnace
    being tested.
    EXAMPLE:
    INPUT: 92,000 BTU/HR
    OUTPUT CAP: 84,000
    Should the figure you calculated not fall within five (5) percent
    of the nameplate rating of the unit, adjust the gas valve
    pressure regulator or resize orifices
    .
    There you have it, Goodman says its OK to adjust gas pressure or resize orifices.

  10. #36
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    Quote Originally Posted by chuckcrj View Post
    The following is from Goodman Service Manual for the GCVC950704;



    There you have it, Goodman says its OK to adjust gas pressure or resize orifices.
    interesting how you left out:

    "ALWAYS CONNECT A MONOMETER TO THE OUTLET TAP AT THE GAS
    VALVE BEFORE ADJUSTING THE PRESSURE REGULATOR. IN NO CASE
    SHOULD THE FINAL MANIFOLD PRESSURE VARY MORE THAN PLUS OR
    MINUS .3 INCHES WATER COLUMN FROM 3.5 INCHES WATER COLUMN
    FOR NATURAL GAS OR 10 INCHES WATER COLUMN FOR PROPANE GAS."

    which is immediately after it.
    "Better tell the sandman to stay away, because we're gonna be workin on this one all night."

    "Dude, you need more than 2 wires to a condenser to run a 2 stage heatpump."

    "Just get it done son."

    Dad adjusted

  11. #37
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    by a
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  12. #38
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    Quote Originally Posted by chuckcrj View Post
    The following is from Goodman Service Manual for the GCVC950704;

    Originally Posted by seatonheating
    Sure, then I'll just raise them up to 4.5 I/wc. Get real man. Save it for the technical forums.


    Doesn't matter as his heat loss is 56,594, looks like I'm fine. So the temp rise numbers it post #30 were just pulled out of thin air and not actually measured? I suspected that. In fact I knew it because it wasn't possible.So what you are saying is that we should be changing out orifices on a brand new furnace?? Why would they mislead and be so far off in rated capacity?



    There you have it, Goodman says its OK to adjust gas pressure or resize orifices.


    Are you dense?? That heat loss is what I came up with per Hvac-Calc, and is no way related to the actual temp rise of the furnace. They are gathered to come up with actual delivered BTU's, not my calculated heat loss. I take this number and adjust my dipswitches accordingly. Are you a rookie who just found a new toy?

    Don't accuse me of pulling numbers out of thin air, ok?? Very insulting and really makes my blood boil. Get lost.

  13. #39
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    Quote Originally Posted by seatonheating View Post
    Are you dense?? That heat loss is what I came up with per Hvac-Calc, and is no way related to the actual temp rise of the furnace. They are gathered to come up with actual delivered BTU's, not my calculated heat loss. I take this number and adjust my dipswitches accordingly. Are you a rookie who just found a new toy?

    Don't accuse me of pulling numbers out of thin air, ok?? Very insulting and really makes my blood boil. Get lost.
    Sorry didn't make myself clear on this one.

    I was in no way reflecting on you load calc, I chose an unfortunate place to put that comment.

    I meant your numbers in post 30 where you gave me temp rise and cfm numbers that gave a higher number than the btus worth of gas actually entering the appliance.

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