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Wanted: Creative Ideas - Oversized Boiler with No Buffer Tank Option

Boilertrouble Member Posts: 14

Our boiler is oversized at 145K BTUs (Burnham Oil MPO-IQ 189) vs. a heat loss calculation of 89K BTUs.  Unfortunately the contractor did a straight replacement of the 28 year old boiler without a heat loss calc.  The cycles are running 3-4 minutes although only turning on a few times per hour.

The house has 4 zones using a hydronic coil blower (3 blowers – upstairs blower shares two heating zones) and an indirect water heater.  The boiler also has an outdoor reset.  Both of those items are making the boiler have even shorter cycles.  The pictures are attached, but unfortunately we do not have space in the finished basement equipment room for a buffer tank.

Thanks to all your feedback and a 45 minute conversation with the Burnham technical team, we came up with the following non-buffer tank options to make the situation better (but not ideal):

  • Burnham recommended not to downfire due to no low fire baffle on this unit.  He is concerned with flue soot issues.
  • Thermostats are set at 68 during day and 63 at night.  We timed all setbacks to go back to 68 at 6am.  The same time we take showers as well.  The thought being to fully load the system at least once per day at 6am.
  • Current minimum using the outdoor reset is set at 110 degrees.  He mentioned moving the minimum up to 130 degrees.
  • Current differential on outdoor reset is 20 degrees.  Thoughts on moving that to 30 degrees for slightly longer run times.  The Burnham tech said that it won’t make much of a difference.  May add 45-60 seconds max added to the cycle times.

Current combustion stats are as follows.  Of note, we have NO visible condensation issues on the new stainless steel flue.

O2 = 5.3, PPM CO = 29, Eff = 89.3, CO2 = 11.72, Stack Temp = 253, Draft = 0.03

Annual oil usage last year was 1,000 gallons.  This year is estimated at 850 gallons.

Do those ideas make sense?  Any other ideas?


  • SuperTech
    SuperTech Member Posts: 2,152
    Combustion analysis numbers look good except for the low stack temperature.  Maybe you can repipe the indirect tank to do a reverse indirect and use the indirect tank as a buffer?
  • Sylvain
    Sylvain Member Posts: 115
    No place for a buffer tank under the garden ground?
    Altough the buffer tank doesn't need to be at the same level as the boiler.

    The buffer tank will not significantly change the total annual boiler run time [consumption] (but you will have to add the buffer tank losses if outside the house).

    Generally, basement finishing is the ennemy of heating systems.
    One has to choose one's priorities ;-)
    LRCCBJ Member Posts: 116
    edited March 4

    Burnham recommended not to downfire due to no low fire baffle on this unit.  He is concerned with flue soot issues.

    It is doubtful that you'll end up with "flue soot issues" with a 1 gallon nozzle on this unit. That's 30% less than the current setup. There is only one way to be sure of that............set it up properly with the 1 GPM nozzle and observe it over a period of time.

    The low stack temperature is definitely a concern, however. I find it amazing that they can manage to get the stack temp down that low. Do you know if that is "net stack temperature" that is displayed.

  • Jamie Hall
    Jamie Hall Member Posts: 23,270
    How necessary to your comfort is it to have the four separate heating zones? If you could rearrange the ontrol logic, together with some real balancing between the zones, could you live with the boiler -- and heating system -- running only when the structure called for heat (all four zones running)? That would bring the load somewhat closer to the boiler power, anyway, and thus allow longer run times and a chance for the boiler to actually warm up...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Derheatmeister
    Derheatmeister Member Posts: 1,527
    edited March 4
    1.Tekmar used to have a PID control that would also Group the zones together therefore reducing the short cycling...
    2. Cast iron heat emitters vs. regular Baseboard.
    3. A Multi Coil reverse indirect such the Latento from IVT. 1 800 873 3507.
  • Sylvain
    Sylvain Member Posts: 115
    edited March 4

    3. A Multi Coil reverse indirect such the Latento from IVT. 1 800 873 3507.

    Aha latent heat storage.
    When latent heat is greater than sensible heat it allows greater storage for a given volume. But the material must change state at the desired temperature and the exchange surface with water will have to be great enough for rapid heat exchange without the equivalent of "freezing" (assuming solid/liquid change of phase).