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Increasing stack temperature

zeke
zeke Member Posts: 223
I am wondering why over the past several years following a tuneup of my 14 year old oilfired furnace, the CO2 level remains 11% but the stack temperature has steadily risen from 350 ( in 1998) to 650. Could anybody tell me the possible causes?

Also I have never seen a tech test for CO. Am I missing something?

Thank you for your reply.

Comments

  • Maine Ken
    Maine Ken Member Posts: 531


    What kind of "tune-up"? Oil side only? Cleanout ports, flue, breech?
  • Steamhead
    Steamhead Member Posts: 14,832
    It's probably sooted up

    Bet they didn't brush it out. Have someone else take a look at it.

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  • Pinball
    Pinball Member Posts: 249


    One more thing, If it is a steel boiler with baffles, are they still there?
    I have seen some "techs" clean a boiler and "forget' to put the baffles back in the unit. or are they have slowly rotted out to the point where they are almost non-existant.
    Either way, have somone else do a real tune-up complete with a bacharach kit or equivelent. Test for First and foremost, DRAFT, smoke, CO2 and net stack temp.
    Al
  • Tony Conner_2
    Tony Conner_2 Member Posts: 443
    Could Also Be...

    ...scaled-up on the water side. Do you have to add much water to this boiler?
  • Bill Nye_2
    Bill Nye_2 Member Posts: 538
    could be

    different nozzle[bigger] air setting, draft, technician, how long the first guy vs the second guy left the thermometer in? Restricted return air flow....blocked register or dirty filter? Adequate ductwork
  • zeke
    zeke Member Posts: 223


    Thank you all for your response.
    To clarify things.It's a forced hot air system and I just moved in. The test results are posted on the furnace panel, with different technicians, so I can't answer the nozzle question or the thoroughness of these tuneups. However, I have personally verified the current 650 degree stack temperature reading. The last tuneup was in April. Can I do anything now as a DIYer to lower the stack temperature or should I wait for
    the next tuneup, since the estimated efficiency as recorded is 81% ( I wonder how good this number is)?
  • Mark Hunt
    Mark Hunt Member Posts: 4,909
    Over-fired or


    insufficient air flow across the heat exchanger.(Air flow would be my bet)

    Make and model of the unit would be helpful, as would a picture of the duct system.

    Hard to diagnose over the I-net.

    Mark H

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  • zeke
    zeke Member Posts: 223


    Mark,
    Thanks for answering.
    The unit is a carrier 58HU085 which is an upflow system with an A/C addition.; the main supply duct is 24x10 and return duct 18x10 into the plenum. The filter is 20x25 and was recently changed. I also measured the hot air leaving the heat exchanger at about 110 to 120 deg. using a 100-800 range temperature dial indicator.
  • Mark Hunt
    Mark Hunt Member Posts: 4,909
    Is the


    burner operating on high limit? That would be on a call for heat, the burner fires, fan comes on after a delay, burner shuts down but fan continues to run and the call for heat is NOT satisfied, burner fires again.

    I'll look up the specifics on that unit.

    Mark H

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  • zeke
    zeke Member Posts: 223


    Mark,
    I think on a call for heat, the burner starts and the blower doesn't come on until 140 is reached and both fan and burner are on until setpoint is reached when burner shuts down, after which fan continues until temp falls to 100 deg. The high safety limit is set at 180.
    Thanks again.

    Zeke
  • Ed N.Y.C.
    Ed N.Y.C. Member Posts: 73
    Hi Stack

    Zeke I am assuming that 650 is a net not a gross, if so than you would be in the range of 16%co2. Sounds like a bogus result. Stacks way too high,should be approx. 450 gross and co2 approx. 11%. Hope this helps. ED N.Y.C.
  • Tundra
    Tundra Member Posts: 93


    Another thing for your check list. Make sure the fan is clean. If it is loaded it will significantly affect the amount of air over the heat exchanger.
  • zeke
    zeke Member Posts: 223


    Ed,

    The 650 is gross, so the net is probably 580.And the CO2 has been consistent at around 11% over many years. Also the blower looks clean.
    What about increasing the blower speed? It may not be on its highest setting.

    Thanks for your remarks.

    Zeke
  • zeke
    zeke Member Posts: 223


    Tundra,
    Sorry I posted under Ed's reply. The blower looks clean.
    Thanks

    Zeke
  • Ken D.
    Ken D. Member Posts: 836
    High Stack

    A number of things cause a high stack. Burner fan must be clean. Blower fan must be clean. Belt tight?. Registers open? Proper nozzle? Proper pump pressure? Air and oil filters clean? Pump strainer clean? Baffles ok? Heat exchanger clean? Good combustion? Burner properly adjusted? Draft too high? Combustion chamber OK? A unit with improper nozzle or combustion can require too much primary air that increases stack temp. Blower speed and rotation OK? Stack temp. gauge accurate? One other remote possiblity- I had a customer once that had miles high stack temp. and terrible combustion. Turns out he would put his used motor oil from his car into the oil tank. I assume you have good fuel. Ken D. with a capital K.
  • A. mitchell
    A. mitchell Member Posts: 8
    dirty heat exchanger

    an 1/8 inch of soot is equal r-30 in your home my guess would be have the unit propley cleaned as the soot build up will result in poor heat tranfer and generate high stack temps
  • Robert O'Connor_6
    Robert O'Connor_6 Member Posts: 299
    What Brand

    furnace is it?

    Regards

    Robert

    ME
  • Jim Davis_3
    Jim Davis_3 Member Posts: 578
    Air Flow

    If your air temperature is only 100-120 degrees your blower is running too fast and this will cause your flue temperature to be 50-75 degrees high. Normal flue temperature for oil should be 490-600 dergrees gross.
  • zeke
    zeke Member Posts: 223


    Just saw a typical tuneup on my neighbors furnace (similar to my foced hot air) and the technician looked at me like I was nuts asking why he doesnt clean the heat exchanger; said he never heard of doing this.
    What do you professionals do?
  • zeke
    zeke Member Posts: 223


    Just saw a typical tuneup on my neighbors furnace (similar to my foced hot air) and the technician looked at me like I was nuts asking why he doesnt clean the heat exchanger; said he never heard of doing this.
    What do you professionals do?
  • zeke
    zeke Member Posts: 223


    I dont get it. If the blower is blowing more air across the heat exchanger my logic says you should be transferring more heat and therefore LOWERING the stack temperature, not increasing it.
    Where did I go wrong?
This discussion has been closed.