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Help with new boiler purchase please

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Comments

  • Gordy
    Gordy Member Posts: 9,514

    Good points. I've been assuming that the boiler is in an unconditioned basement, so losses there don't help to heat the structure.

    If the stack damper doesn't help that much with efficiency (1%), does that mean that we don't really lose much of the heat stored in the boiler due to an open stack, or that the dampers just aren't that good?


    The dampers don't seal 100%. There is still conductive losses of the metal flue pipe.
  • Leonard
    Leonard Member Posts: 903
    edited February 2017
    At 1% loss stack damper losses sound insignificant. If your burning 1200 gal/year of oil thats only ~ $24/year. If retrofit long break even, ROI.

    Seems a non-modulating burner provides a fixed mass flow of fixed temperature hot gases to the boiler.

    Basically the boiler is an air/water heat exchanger , so if the water temp is higher then the stack exhaust temp will be a little higher ( lower overall efficiency).

    If your load ( radiators) can only take 50% of boilers BTU/hr output, then boiler water temp will just rise till burner shuts off on hi-limit. Basically your in a cycling mode. Your not going to see the other 50% go up the chimney while burner is running.

    With modulating burner seems at low firing rate the amount of hot gases (mass flow rate) from burner into boiler is lower, this allows the hot gasses to remain in contact with the water jacket longer. Giving them more time to give up their heat. Seems this should result in a lower exhaust stack temp. ( less % of fuel's BTUs lost up the chimney)

    Question becomes how much fuel can you save doing this and is it worth it given equipment and maintenance costs. I have no idea, you have to look at the charts, make assumptions, and run the numbers. Or talk with guys here.
  • FastEddie
    FastEddie Member Posts: 14
    @Paul48 I have no issues with discussions that pertain to what i was asking. This forum has been a huge help to me and i appreciate everything. Besides while some of this discussion is above my head, its great knowledge for anyone else out there looking for this information.

    I've pretty much decided on the Viessmann CU unit that @Hatterasguy suggested to me. The cost of it after rebates was still very good (much lower than every other companies options!!! -see above-) after speaking with Bob about the unit and how its constructed and the maintenance, i felt good about the system.
  • Gordy
    Gordy Member Posts: 9,514
    Let's visit stack temp. Even at 180 supply water temp the stack temp in a mod/con with plastic venting. Try that with a Ci boiler....
  • Paul48
    Paul48 Member Posts: 4,469
    @FastEddie
    Thanks! I agree about the discussion. Sometimes folks don't like it though, and after all, it's their post. There's something to be learned, every day.
  • Brewbeer
    Brewbeer Member Posts: 616


    There is the ongoing suggestion that more comfort is available from a system that runs continuously.

    I'm going to make the counter argument that 95% of the people wouldn't know whether their boiler is running continuously or whether it is cycling.

    The 'stat typically has differential of 1.5F. You'd be hard pressed to get a continuously running system to stay within that range (although, I agree, some have done it). Now, if you achieve it, can the average person notice the narrowed differential?

    My conclusion is they cannot.

    95%? That's 19 in 20. I don't agree with that assessment, but I'm open to seeing some data that could change my mind.

    Don't overlook the noise factor. I can hear my boiler running when it's firing at 100%. I can't hear it running below 50% fire unless I'm in the basement. Also, fin tube baseboard can have a tendency to click and ping with changing temperatures due to expansion and contraction. With the mod con, baseboard temps stay more constant, which really cuts down on expansion noise.
    Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
    System Photo: https://us.v-cdn.net/5021738/uploads/FileUpload/79/451e1f19a1e5b345e0951fbe1ff6ca.jpg
  • Paul48
    Paul48 Member Posts: 4,469
    Comfort for one person, can be very uncomfortable for another. Try and tell an 80 year old woman with arthritis, she's better off without that piping hot radiator. Just sayin'
  • Leonard
    Leonard Member Posts: 903
    edited February 2017
    If your near the radiator high water temps can make the area around radiator feel warmer than room is on average.

    I've got my desk against a wall with baseboard along it. My feet are near the baseboard. And I believe hot air rises off the baseboard hits bottom of desk and flows towards me.

    I noticed it feels colder now that I reduced by boiler hi setting from ~ 210 to ~ 170 even though wall thermostat says it's ~ same temp ( I previously had leaking DHW mixing valve that made shower cold)

  • hydro_newbie
    hydro_newbie Member Posts: 37
    Back to Gordy's charts...would folks agree that the likely rationale for showing drastically reduced efficiency for a fixed-output CI boiler is due to an assumption that the BTUs used to heat the boiler are lost between cycles?
  • Jamie Hall
    Jamie Hall Member Posts: 19,935
    Of course, if the basement is under the house (most of them are), any heat lost to the basement is going to find its way up into the house. If you don't believe me, ask my cat -- she lies on the dining room floor right over Cedric most of the day!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Paul48
    Paul48 Member Posts: 4,469
    Hat.......Then what happens to the energy? Isn't the raised ambient of the basement then utilized by the conditioned space in the form of reduced heat loss? Minus the losses to the basement exterior.
  • Jamie Hall
    Jamie Hall Member Posts: 19,935
    Cedric really isn't that massive -- a Weil McClain 580 -- and is well insulated.

    However, there is an interesting point here. The basement is warmer than it would be without Cedric (and, at each end, two large condenser radiators!). But then, as a result, the floors over the basement are also warmer than they would otherwise be. This does represent heat lost from Cedric -- and suggests that, considered all by itself, Cedric isn't as efficient as it should be. However, if that heat weren't provided by Cedric it would have to come from somewhere, or the basement would be much cooler (colder!) and so would the floors. Which would be undesirable. The only losses from Cedric which are undesirable are the losses up the chimney -- at least in my view.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Jamie Hall
    Jamie Hall Member Posts: 19,935
    No argument. None at all. Might I enquire, though, what was the temperature in the basement under the two conditions?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Matt_67
  • Jamie Hall
    Jamie Hall Member Posts: 19,935
    It's not so much the basement temperature over the year -- and the situation will be very different for different situations. In some -- such as the place I care for -- having the residual heat from Cedric (and the water heater) in the basement in the winter is helpful, since it keeps most of the basement warm enough to keep working down there (though there are corners where the temperature at floor level gets down to freezing -- or even below on really cold windy nights!) and my workshops are down there. I'd have to have other heat in the workshop areas if it weren't there. So in my situation the "lost" heat isn't lost at all.

    In other houses or buildings, it might be that there is deliberate heat installed in the basement -- or that there is nothing in the basement which needs to be kept vaguely warm (I wouldn't call my basement warm, exactly...) -- and then the residual heat from the boiler might be thought of as wasted.

    I would note in passing, for others who may be reading this debate, that we aren't talking about insulating steam mains! They absolutely need to be insulated, and mustn't be thought of as contributing useful heat to anything. Not so much because the heat might or might not be useful, but because an uninsulated steam main really messes of the speed and evenness of distribution to the rest of the system.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Eastman
    Eastman Member Posts: 927
    A damper only improves efficiency by 1%? Where is this coming from? Do they simply not work very well or is there nothing to be saved?
  • Eastman
    Eastman Member Posts: 927
    I think cast iron boilers should be undersized by at least 20%. Then on design day they should be about 100% efficient.
    Paul48
  • FastEddie
    FastEddie Member Posts: 14
    @Hatterasguy What exactly is the SWT at design? I didn't ask this but i can when he comes in the next week or so to do the install. He said the boiler should be here in a few days.

    I also decided to use him to install a Ductless Mini Split system for the house. He recommended going with the Daiken units for that (which is also something i am new too).

    I appreciate everyone's help and comments on the thread. Without your guidance i was leaning toward the Bosch Unit which would seem like i would have been disappointed with.
  • HVACNUT
    HVACNUT Member Posts: 4,762
    That's quite a discussion boys.
    Long story short, a mod con is best served with large mass radiators and or low temp radiant, otherwise your not achieving the stated efficiency. (We all know AFUE is bs for boiler ratings anyway. Only good for furnaces).
    My choice, high and low temp is a Buderus G115 with thermostream, 3" of insulation, even on the bottom, the 2107 Logamatic with ODR and hydraulic separation.
    Mike drop!
    I wish they still imported the 125BE.
    That system is wicked awwwsome.
  • Gordy
    Gordy Member Posts: 9,514
    @HVACNUT You do know that this post is in the gas heating categorey. The G115 is an oil boiler.....
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 12,637
    I think the cast iron efficiency plummets due to standby loss when it starts to cycle on low load. Jacket and stack loss.

    The mod con matches the input to the load so standby loss is reduced. A mod con sized so it's minimum input will be less than the smallest zone would be a good thing

    Not pickin sides and not sold on mod con until we know more about there longevity

    But I installed a couple of Teledyne Larrs 9600s on a job 14 years old still running not the best boiler in the world

  • HVACNUT
    HVACNUT Member Posts: 4,762
    > @Gordy said:
    > @HVACNUT You do know that this post is in the gas heating categorey. The G115 is an oil boiler.....
    I want him to convert to oil. Lol. Should've realized with the mod con talk. Sometimes my brain goes into restricted areas.
  • FastEddie
    FastEddie Member Posts: 14
    SWT on the coldest day this year (which just so happened to be the day after the boiler was installed) was mid to low 20's and it was at 147. The next day when it was mid 30's here the SWT was 131.

    Hope that's the info your looking for.
  • bink
    bink Member Posts: 97
    Just another input wondering what kind of chimney you have outside the house or inside - lined? I had a Buderus G115/4 installed then found output flue gas temperature of 300 degree was too low for my clay lined chimney. I have oil system. Had to install a stainless liner. Just want to make sure all the bases are covered. Lots of input but you're doing the correct thing by asking questions,
    Rich
  • FastEddie
    FastEddie Member Posts: 14
    i have an outside based chimney. However, i don't remember if we used it or not. I think it was routed straight outside. I will have to double check.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited March 2017
    Any boiler no matter it's type or brand has one job.. Make energy. The amount of energy to enter into the space is dictated by the emitter. What moves the energy from the boiler to the emitter is a circulator. Of the 3 which is most important?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Gordy
    Gordy Member Posts: 9,514
    edited March 2017
    Emitter. With out it nothing happens. Type, and sizing will dictate the performance of the "system".
  • Paul48
    Paul48 Member Posts: 4,469
    :smile:
  • Steamhead
    Steamhead Member Posts: 15,646
    Gordy said:

    1% efficiency gain from stack damper.

    That depends on what kind of chimney it's hooked into. A chimney built in the last 30-40 years, maybe. But an older chimney designed for a coal-fired boiler can develop a lot of draft, which can cool down a boiler in no time at all. In that case, a stack damper helps a lot.

    I've never seen this 1% figure backed up by a description of how they came up with it. So we should take it with more than a few grains of salt.
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
    Consulting
    Gordy