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Is My Boiler Operating Efficiently? Take a look at my data

MichaelG Member Posts: 26
Call me a nerd, but I added some "smart" monitoring of my old relay-controlled heating system and I want to know what people think of its operation.

It's a 4-zone hydronic baseboard system oil-fired with separate circulator pumps (no valves). The boiler is set up with a lo/hi limit aquastat.

Take a look at the attached chart of the boiler firing (top line) compared to the calls for heat from two zones, shown below. When I look at it, I notice the following:
  • The long pulses of the boiler firing occur at the beginning of a call for heat, when the zone is cold and more heat is needed for longer.
  • After the zone is heated up, the boiler cycles on and off periodically (bouncing off the high limit) until the set point is satisfied. The "on" cycles tend to be 2-3 minutes, which is long enough to go from the high limit cut-in back up to the high limit.

Is this proper operation for a system like this? Since the boiler has no way to throttle its output based on the heat requirement (1 zone running vs all 4), it seems the only way for it to run is bouncing off the high limit.

One thing I've considered is raising the high limit from 190 to 200 and increasing the high limit diff from 10 to 20. This would effectively double the length of the cycles and reduce their frequency by half.

Thanks everyone! In case you're wondering, the logging is done with a combination of:
  • Samsung Smartthings 2 Hub (which can control Z-Wave devices)
  • Some relays to create dry contacts to monitor (for example a relay controlled by B1 on the aquastat)
  • Aeon Labs ZW097 Dry Contact Sensor for each monitored input (talks to the Smartthings hub)
  • InitialState to log and chart the data


  • SuperJ
    SuperJ Member Posts: 609
    edited March 2018
    2-3 minute cycles are pretty short. I would drop your cut in temperature quite a bit. For the high limit 190F is pretty hot already, not sure about going to 200F. Since your system is running so hot you could probably let it drop to 140-160F before it cuts back in.

    You may want to consider an outdoor air temperature reset, this will create longer demands for heat since the output of the emitters drops as the water temperature goes down. You will have more time with overlapping calls for heat, which will add thermal mass (higher volume of water circulating) to the system and lengthen your run cycles.

    You could set it up so that it can't run until 2 zones are demanding.

    I'm assuming your layout is primary secondary, with a secondary pump for each zone?
    Do you have a buffer tank? Looks like your either zoned tightly enough/oversize enough to warrant a buffer tank.

    Everytime your boiler cycles, it's inefficient, and your hx goes thru and expansion and contraction cycle (you only have so many, even if you have a lot in the lifetime of a boiler). The vent motor blows cold air thru the boiler to purge it (wasting heat up the chimney), and you may not dry out condensate produced at the start of a run cycle leading to other problems.
  • SuperJ
    SuperJ Member Posts: 609
    I would drop your cut in temps until you basically have a continuous call for heat from at least one zone (or have a zone temp not maintain setpoint), or you've hit your boiler's safe minimum RWT.
  • NY_Rob
    NY_Rob Member Posts: 1,370
    What type of radiation do you have- fin-tube, cast iron, etc... ?
  • MichaelG
    MichaelG Member Posts: 26
    Emitters are fin tube baseboard
    EBEBRATT-Ed Member Posts: 15,849
    @MichaelG ,

    Have your burner checked to see if it can be down fired with a smaller nozzle. A good technician and combustion testing is required. Leave the high limit @190 and increase the differential to 30-40 deg if you can. If this does not reduced the cycling consider a buffer tank