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Boiler efficiency

Pegret
Pegret Member Posts: 37
It's been determined that my new boiler is larger than it needs to be: approx. 2.25 times too big. How much does this effect the efficiency? It's running fine but I'm concerned I'm not getting the efficiency improvement I wanted with a brand new boiler.

Comments

  • SuperTech
    SuperTech Member Posts: 1,691
    Yes. Oversized boilers don't operate efficiently and sometimes run so poorly that it's detrimental to the lifespan of the boiler, short cycling, flue gas condensation.
    ComfEffic
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,342
    What @SuperTech said
  • Pegret
    Pegret Member Posts: 37
    Thanks. There's no way the man who installed it is going to replace it. Is there any way to modify this oversized boiler?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,342
    If it's gas a qualified technician may be able to install a two stage gas valve....depends on the boiler.

    If oil it can probably be down fired somewhat by someone that knows what they are doing.

    I am assuming the boiler is steam since you posted in "strictly steam"

    You say it is running well. If you watch it run on a cold day in the basement how many time does the burner go on-off in an hour?
    PegretComfEffic
  • Pegret
    Pegret Member Posts: 37
    It's gas, steam boiler. I have found a qualified tech and willl ask him about 2 stage gas valve. And I'll time how often it runs per hour. Thank you!
  • SuperTech
    SuperTech Member Posts: 1,691
    How is it vented? If it's vented through a chimney make sure the burner runs long enough each cycle to avoid flue gas condensation. You want to see around 400-450 degrees minimum to avoid condensation.
    ComfEffic
  • pecmsg
    pecmsg Member Posts: 2,342
    Pegret said:

    It's been determined that my new boiler is larger than it needs to be: approx. 2.25 times too big. How much does this effect the efficiency? It's running fine but I'm concerned I'm not getting the efficiency improvement I wanted with a brand new boiler.

    How was this determined?

    Downsizing a small % can generally be done. 50% or more I Doubt It!
    ethicalpaul
  • ethicalpaul
    ethicalpaul Member Posts: 3,137
    edited February 2019
    "efficiency" is an interesting term. Just curious, what difference did you expect when going to this new boiler? Like, a dollar savings?

    What model is it and what did it replace?

    (I've been extra-vigilant about this term ever since I was telling a physics professor/alt energy fan friend of mine about my "inefficient electric water heater" and he opened my eyes by saying "electric heat is 100% efficient." He's not wrong, but it feels inefficient when it costs twice as much as a NG unit to heat water!)
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    ComfEffic
  • PMJ
    PMJ Member Posts: 1,122
    A properly set up boiler runs at its rated efficiency when it is running. That fact is not changed simply by its size relative to the system it is connected to. The bigger the boiler is the smaller percentage of the total time it will have to run then to heat the structure, that is all. Properly controlled, and by that I mean not allowing a big boiler to generate unnecessary pressure in the system, there is no loss in efficiency to worry about.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
    ethicalpaul
  • ethicalpaul
    ethicalpaul Member Posts: 3,137
    I agree @PMJ that is the definition of "efficiency" but I bet @Pegret is also interested in the efficiency of his money getting converted into household heating.

    And I think that is the real nature of his question which might be: "How can I most economically operate a boiler that is possibly twice the size it needs to be, while trying to ensure it doesn't have a shortened service life?"
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    ComfEffic
  • PMJ
    PMJ Member Posts: 1,122

    I agree @PMJ that is the definition of "efficiency" but I bet @Pegret is also interested in the efficiency of his money getting converted into household heating.

    And I think that is the real nature of his question which might be: "How can I most economically operate a boiler that is possibly twice the size it needs to be, while trying to ensure it doesn't have a shortened service life?"

    Operating a boiler exactly oversized like @pegret's boiler is what I have been doing for the past 27 years. And that boiler I am still operating already had 36 years of operation on it when I got it. So I think I can say with some authority that extra size and extra cycles are not a concern with respect to service life.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
    ethicalpaul
  • pecmsg
    pecmsg Member Posts: 2,342

    "How can I most economically operate a boiler that is possibly twice the size it needs to be, while trying to ensure it doesn't have a shortened service life?"

    First by finding out what size is actually needed. Then and only then can #'s be run.
    With that information the OP Can determine can it be downsized and what is the return on investment or replace and return on investment!
  • PMJ
    PMJ Member Posts: 1,122
    I downsize my boiler by controlling the run time. Dramatically less expensive way to go about it than special burners, dramatically more adjustable too.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
    ComfEfficDave in QCA
  • ethicalpaul
    ethicalpaul Member Posts: 3,137
    PMJ said:

    Operating a boiler exactly oversized like @pegret's boiler is what I have been doing for the past 27 years. And that boiler I am still operating already had 36 years of operation on it when I got it. So I think I can say with some authority that extra size and extra cycles are not a concern with respect to service life.

    Thank you, and that sounds great, but I bet his boiler isn't 63 years old :)
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    ComfEffic
  • PMJ
    PMJ Member Posts: 1,122

    PMJ said:

    Operating a boiler exactly oversized like @pegret's boiler is what I have been doing for the past 27 years. And that boiler I am still operating already had 36 years of operation on it when I got it. So I think I can say with some authority that extra size and extra cycles are not a concern with respect to service life.

    Thank you, and that sounds great, but I bet his boiler isn't 63 years old :)
    Right. I was telling him not to worry about having a large boiler be the cause of reduced efficiency or service life.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
  • ethicalpaul
    ethicalpaul Member Posts: 3,137
    I get it, but I imagine yours is built differently than his, which might be more prone to damage from short cycles?
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    ComfEffic
  • PMJ
    PMJ Member Posts: 1,122
    > @ethicalpaul said:
    > I get it, but I imagine yours is built differently than his, which might be more prone to damage from short cycles?

    I think it is safe to assume today's boilers won't survive a small fraction of the number of years or cycles my boiler has run. I also think it safe to assume that protecting today's boilers from "short" cycles (whatever those are) will make up the difference.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
    ethicalpaul
  • Attached is a efficiency curve that is often referenced if using atmospheric boilers with no stack damper. I have found it quite accurate for predicting fuel savings when reducing boiler capacity to proper levels. Oversized atmospheric boilers on steam systems can be particularly inefficient because the radiators installed in most buildings between 1900 and 1940 are also about 60% oversized for the heating load. The typical steam boiler sized to radiation with a standard 33% pick up factor will have about twice the capacity necessary to heat a building on the coldest day. If your boiler is 2.25 times the size required for the radiators, you may be about 4.5 times oversized for the heat load. This would yield a seasonal efficiency around 52%, assuming a steady state efficiency around 78% ( which is realistic number for most modern atmospheric steam boiler). A stack damper may help this number some under the right conditions
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    ethicalpaulSuperTechComfEfficttekushan_3
  • SuperTech
    SuperTech Member Posts: 1,691
    > @PMJ said:
    > > @ethicalpaul said:
    > > I get it, but I imagine yours is built differently than his, which might be more prone to damage from short cycles?
    >
    > I think it is safe to assume today's boilers won't survive a small fraction of the number of years or cycles my boiler has run. I also think it safe to assume that protecting today's boilers from "short" cycles (whatever those are) will make up the difference.

    Short cycles can be defined as a cycle where the burner fires up but doesn't stay on long enough to heat up the chimney enough, allowing condensation to form. Also any equipment constantly turning on and off will wear out faster than normal, leading to breakdown.
    ComfEffic
  • PMJ
    PMJ Member Posts: 1,122
    > @The Steam Whisperer said:
    > Attached is a efficiency curve that is often referenced if using atmospheric boilers with no stack damper. I have found it quite accurate for predicting fuel savings when reducing boiler capacity to proper levels. Oversized atmospheric boilers on steam systems can be particularly inefficient because the radiators installed in most buildings between 1900 and 1940 are also about 60% oversized for the heating load. The typical steam boiler sized to radiation with a standard 33% pick up factor will have about twice the capacity necessary to heat a building on the coldest day. If your boiler is 2.25 times the size required for the radiators, you may be about 4.5 times oversized for the heat load. This would yield a seasonal efficiency around 52%, assuming a steady state efficiency around 78% ( which is realistic number for most modern atmospheric steam boiler). A stack damper may help this number some under the right conditions

    Thanks for this @The Steam Whisperer .

    The key note here is "no stack damper". These devices are absolute game changers. Efficiency on a cycling boiler is not close without one.

    When I moved in there wasn't one. 10 inch flue and tall chimney. It was like a powered blower cooling down the boiler between cycles. I installed one and it proved to be the single biggest change I made. Time to steam many minutes shorter each and every cycle.

    Now that I have reduced time to steam even further with vacuum between cycles I believe the size of the boiler to be a non issue with regard to efficiency. In fact, to enjoy the benefits of vacuum you need off time. This requires a big boiler.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
    ttekushan_3
  • Motorapido
    Motorapido Member Posts: 237

    A stack damper may help this number some under the right conditions

    About stack dampers -- my anecdotal experience when I replaced a broken automatic stack damper (it was switched off and left in the fully open position by the prior house owner) with a functioning stack damper was a significant increase in my boiler room air temperature. I assume that before replacing the damper, the flue was continuing to draw warm air out of the basement and up the chimney. I figure that a warmer boiler room means a warmer boiler between calls for heat, which translates into quicker times from start-up to steam production, and thus energy savings. This is purely anecdotal since I'm not an engineer or scientist of any sort, although measured accurately with the temperature sensors in my basement and boiler room (part of my smart home system of sensors).
    ethicalpaul
  • PMJ
    PMJ Member Posts: 1,122
    @SuperTech said:

    "Short cycles can be defined as a cycle where the burner fires up but doesn't stay on long enough to heat up the chimney enough, allowing condensation to form. Also any equipment constantly turning on and off will wear out faster than normal, leading to breakdown".

    I do a lot of 5-9 minute burns 3 times an hour and don't have condensation problems. I guess the chimney stays warm enough all the time running this way.

    I must ask then also is 3CPH "constantly turning on and off"?

    All I am trying to do here is allow homeowners to relax a little with regard to fears about boiler size and more cycles as it is pretty regularly suggested here that they should be very worried about these things. I think I am on pretty firm ground with a lot of evidence that such concerns are unfounded. Here we have an OP who just spent a good sum on a new boiler concerned he made a big mistake. I think we should be assuring him he did not. I will tell him that if no one else will. I have some pretty good results with a boiler sized pretty much like his to back me up.

    That boilers are much more cheaply made these days and won't last as long anyway is a different subject.



    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
    SuperTech
  • ethicalpaul
    ethicalpaul Member Posts: 3,137
    edited February 2019
    With respect, your pretty good results are at least partially due to you having a boiler that is built way better than anything today, I don't see how that's a different subject :)

    But I agree with you in general, his boiler can probably do a fine job for many years. But it is a valid concern, having a boiler 2.5 times the size it needs to be, and worthy of thought and discussion of running it as well as possible to minimize short and long term costs. I think it's very possible that people here can help the poster have a nice system that maybe doesn't even short cycle.

    I'm still curious what model it is, because there are definitely some that can be adjusted after the fact, I have learned even after my short time here.
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
  • The Steam Whisperer
    The Steam Whisperer Member Posts: 760
    edited February 2019
    From my own experience I tend to agree regarding the potential improvement due to a stack damper, especially with oversized equipment. However, several studies for large multi-unit buildings have shown only small benefits in reduced as usage. In my own experience on one of my family's properties, we saw a boiler room go from near freezing in extreme cold ( out door air intake grill without damper), to probably over 100F with a damper that didn't even close very tightly. That has to translate into savings
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    ethicalpaul
  • PMJ
    PMJ Member Posts: 1,122
    edited February 2019

    From my own experience I tend to agree regarding the potential improvement due to a stack damper, especially with oversized equipment. However, several studies for large multi-unit buildings have shown only small benefits in reduced as usage. In my own experience on one of my family's properties, we saw a boiler room go from near freezing in extreme cold ( out door air intake grill without damper), to probably over 100F with a damper that didn't even close very tightly. That has to translate into savings

    Agreed. In my experience this is not even close. An open flue makes sense only with a coal fire. Today anyone running without a damper is doing this the hard way.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
  • Kjmass1
    Kjmass1 Member Posts: 212
    I had the same questions with my 45+ year old steam boiler. Runs fine, but old. See my post here with some technical info from Dana on why you are better off insulating and improving envelope before replacing a steam boiler.

    If you really want to save money- superinsulate and tighten up the house, attic, and basement walls and sills. Get room by room Man J done. Replace radiators with smaller, more appropriately sized ones for the load. Then downsize boiler.

  • Jamie Hall
    Jamie Hall Member Posts: 17,122
    Kjmass1 said:

    ...

    If you really want to save money- superinsulate and tighten up the house, attic, and basement walls and sills. Get room by room Man J done. Replace radiators with smaller, more appropriately sized ones for the load. Then downsize boiler.

    All that is sometimes possible. Sometimes not.

    That said, I'd take a really close look at what @PMJ is suggesting regarding using a timer to effectively downsize the boiler. There are various ways to set the timer -- but I'd start by seeing how long it takes to get the slowest (not necessarily farthest) radiator hot, and -- in this case with a boiler twice what it needs to be -- set the on and off times to that, and then fiddle from there. Let your thermostat be the overall control... and keep the pressure and low water controls and safeties, of course.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • PMJ
    PMJ Member Posts: 1,122
    @Jamie Hall ,

    It would be great if people would think about this some and try their own thing. More than one way to do it and the equipment is really inexpensive.

    For a few years now I have taken the guesswork out of the first burn on a new call and installed an adjustable temperature switch on that last rad to get steam. Since every burn is different depending on how long the burner has been off one way is to have every new burn run until you get steam to that remote rad plus an adjustable time for an approximate fill level of your choice. Then a minimum time off before the next burn can start(or currently I like when that temp switch opens up again). As long as the net duty cycle here easily covers your coldest day everything is covered. In this way the boiler size is effectively reduced. It will still be filling rads more than needed on an average day but far less than what it was running either to tstat satisfaction or vaporstat stop. A few more cycles, less swing, more even heat. With this approach it really doesn't matter how big the boiler is. You just need a delay off/delay on timer and the temp switch. Maybe $150.

    There really are many options here once one gets away from thinking about the boiler itself and instead about how long and when it runs. Move this onto a PLC platform and there is no limit to what logic you can try with just keystrokes. And remember - none of the basic safeties are changed or bypassed. They will still protect the system just as they do now.
    1926 1000EDR Mouat 2 pipe vapor system,1957 Bryant Boiler 463,000 BTU input, Natural vacuum operation with single solenoid vent, Custom PLC control
    ethicalpaul
  • Kjmass1
    Kjmass1 Member Posts: 212
    Any way to use ecobee remote sensors/minimum run time settings/temp swing to do a similar thing?
  • mikeg2015
    mikeg2015 Member Posts: 1,183

    A stack damper may help this number some under the right conditions

    About stack dampers -- my anecdotal experience when I replaced a broken automatic stack damper (it was switched off and left in the fully open position by the prior house owner) with a functioning stack damper was a significant increase in my boiler room air temperature. I assume that before replacing the damper, the flue was continuing to draw warm air out of the basement and up the chimney. I figure that a warmer boiler room means a warmer boiler between calls for heat, which translates into quicker times from start-up to steam production, and thus energy savings. This is purely anecdotal since I'm not an engineer or scientist of any sort, although measured accurately with the temperature sensors in my basement and boiler room (part of my smart home system of sensors).
    An open flue does several things:

    1) it makes the basement negative so increases air leaks at the sill plate. Some of this increases leaks at 1st floor baseboards.

    2) A warmer boiler room acts as radiant heat for the room above. In my home it’s below the kitchen (common since your live-in servant had to stoke the coal fire regularly, My lamainate floors are toasty warm when it’s under 20F outside.

    3) Chimeny stays warmer between cycles. Some of that heat is recovered (if chimney is inside the home) and it extends the life on masonry and chimney liners. My chimney heats some of my cupboards in my kitchen. It should also increase draft on startup.

    Side note - Negative basement will increase radon levels (if that’s an issue in your area).


    However, dampers are not air tight, so there’s still some air leakage especially with taller chimneys. So there’s still an advantage to right sizing.


    I’ve decided ot experiment with a 2 stage gas valve this weekend. Combined with plugging 2 orifices it will have output down to about 56% of nameplate. Will put output before pickup about equal to radiation without TRV’s factored in.

    FOr control I’m going to use a snap switch to allow high stage when the header is cold. OFF 130F, ON 110F. I could us a temperature switch, but those cost $55 vs, a $6 snap switch.



    ethicalpaul