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miller furnace

jim_160jim_160 Posts: 24Member
I have a miller furnace model M1 w/ horizotal heat exchanger. The draft is 0. Complaint of smelly blue smoke coming out of chimney. I checked pump psi= 100. I increased it to 140 and smoke cleared up. I still had 0 draft. I tore down burner ,fan, and plennums to expose heat exchanger. It looked fine. I snorkeled out exhaust tubes rapping them as i vacuumed. No soot build up. Put everthing back together, Still 0 draft! I went up on roof, exhaust vent is good condition and intake air vent is in good shape. My pump psi is 140-- pump cut-off is good --cad cell resistance around 600-800,-- ignitor good. It fires up and runs good but can't get draft. Should I be concerned


  • meplumbermeplumber Posts: 678Member
    Are you sure your manometer is good?

    Just asking....
  • lchmblchmb Posts: 2,932Member
    edited January 2012

    size nozzle are you running in the unit? And is it constant ignition?

    Here is some set up info for Miller's unit

    It is recommended that the Co2 and Smoke levels be

    measured for maximum performance. CO2 readings should

    be 10 - 11% for 66,000 BTUH furnaces and 12 - 13% for

    86,000 BTUH furnaces. The Smoke should be N0. 0 on

    the Bacharach Scale, and 0 to 0.02 negative draft over fire.
  • jim_160jim_160 Posts: 24Member
    nozzle size

    Thanks for the reply

    The nozzle size is .50 80 A. I did not do a combustion test. The pump psi is  140 and cut off is holding with in 10 %. Do I use the site port over fire for all combustion test?
  • jim_160jim_160 Posts: 24Member


    The ignition is not constant. The pump is a clean cut style
  • nugsnugs Posts: 77Member

    Did you pull the burner and fire-box out and check for scale build up at the bottom of the exchanger?    And..........

    Take a CO reading at the breach with the fan off and then the fan on.  If it changes you have a crack in the exchanger.

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