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Good advice for new boiler?

Dan_15
Dan_15 Member Posts: 388
> is simply a way for the boiler to adjust its <BR>
> capacity to the load. I cannot fathom a reason <BR>
> why modulation would a negative feature. It would <BR>
> be like always driving your car the same speed, <BR>
> no matter what the differences in each trip. <BR>
> Doesn't really make sense, does it. <BR>
<BR>

Comments

  • Dan_15
    Dan_15 Member Posts: 388


    I am upgrading my early 60's Burnham gas boiler and am getting conflicting advice. I will have six zones, two cast iron baseboard, one copper baseboard, and three floor radiant (dry). I am looking at the new technology High Efficiency 90+ condensing & modulating boilers. All advice concurs with the high effeciency condensing but then differs on need for modulation because of the different zone types and water temps. Is simpler better? Am I giving up effeciencies? Would appreciate all opinions.
    Thanks,
    Greg
  • Tim_24
    Tim_24 Member Posts: 53
    Modulation

    is simply a way for the boiler to adjust its capacity to the load. I cannot fathom a reason why modulation would a negative feature. It would be like always driving your car the same speed, no matter what the differences in each trip. Doesn't really make sense, does it.
  • Dan_15
    Dan_15 Member Posts: 388
    Sorry, let me explain further.

    By simpler they refer to using a High Efficiency condensing boiler, but not necesarily a modulating boiler that has the newer tech -smaller stainless burners and require a primary loop piping. The water temp will have to maintain higher and burn more then a pure radiant floor system (lower temps)the might warrant full modulation. Simpler to pipe and maintain. Seems logocal if i'm not giving up to much in efficencies for my specific system. But I don't have the experience. Thanks for opinions.
  • Chuckles_4
    Chuckles_4 Member Posts: 43


    Is "Greg" the same as "Homeowner"? Your posts are quite confusing. There are hardly any condensing-but-not-modulating boilers (the Monitor MZ is the only one that comes to mind). It also seems that you are confusing modulation (which refers to varying the output of the gas burners) with varying the water temperature. These are two completely different things.

    You can choose to have low water temperatures without modulation (the burner just goes on and off as needed). And you can have high water temperatures using a modulating boiler (it tries never to turn the burner off, but rather it turns the burner up or down as needed to maintain the chosen water temperature).

    Is the contractor confusing you, or is he confused himself? If the latter, get a better contractor.
  • Dan_15
    Dan_15 Member Posts: 388
    A little confused!

    Sorry to spread my confusion. The contractors seam knowledgable, I'm trying to understand. Was originally looking at a Trinity, Munchkin type of high tech boiler upgrade and was given quotes for what I thought I originally wanted. But another alternative from someone who sells both came back recommending the Utica UB-150 for the reasons I so poorly tried to explain.

    http://www.uticaboilers.com/pdfs/Brochures/BROC Utica UB90-200.pdf
  • Chuckles_4
    Chuckles_4 Member Posts: 43


    The Trinity is a condensing, modulating boiler. The Utica appears to be a condensing-but-not-modulating boiler.

    Your contractor is pushing the Utica and so seems to have suggested that in a "mixed" system, modulation is not useful. This is incorrect. Modulation is always a good thing. It is probably particularly good in a system like yours, with a large number of zones, because you are likely to get short cycles if you don't have a Tekmar or similar device to manage the different heat calls. (You get short cycles because the boiler has to be big enough to run all six zones at once, but often only one zone will call for heat. Short cycles=bad. Short cycles with modulating boiler=not as short=not as bad.

    On the other hand, an argument can be made that in a mixed system, condensing is not so useful. This is because your fin-tube zone will need very hot water, and you won't get condensing and so you won't get the claimed efficiency if the boiler is making very hot water. That's a long-runnign discussion on this board; many will say that a condensing boiler may not give you as much benefit but it still gives you some benefit.

    How is your contractor proposing to get different water temperatures to the different zones? Or is he going to set a high water temperature and just use on-off through six thermostats?
  • Dan_15
    Dan_15 Member Posts: 388


    All have pretty much suggested the same thing. The first three zones of the supply would be pumped to the baseboard zones (copper,cast,cast) then a mixing valve and then pump to the radiant floor zones.
  • Chuckles_4
    Chuckles_4 Member Posts: 43


    OK, that's good. But you're not going to see much condensing. Modulation, on the other hand is still good. Maybe you need a modulating but not condensing boiler, like the Baxi Luna.
  • Constantin
    Constantin Member Posts: 3,796
    Chuckles,

    Wouldn't the degree to which the system will experience condensation depend largely on the heating enevelope vs. the size of the emitters? We don't know anything about the house insulation, nor the amount of baseboard...

    The condensing boiler might make perfect sense for the system mentioned above, particularly if the baseboard is generous enough to operate at 140°F on a design day. Ditto for the radiators. Plus, the slab may pull it all down further into the condensing range... So far, it sounds to me like the contractors know what they're doing (multiple temps, etc.)
  • Chuckles_4
    Chuckles_4 Member Posts: 43


    Theoretically, OK. In practice, few homes have enough baseboard to operate at 140F on a design day...both because of cost and because in many rooms there isn't enough usable perimeter. Both today and 100 years ago, home builders didn't foolishly run up their costs by putting in more radiation than needed. Now with old-fashioned radiators, over time there have been changes which result in homes now having an excess of radiation. But baseboard is modern.

    So while I can't prove it in a court of law, I can make a pretty good guess that the OP's baseboard isn't enough for 140F operation. It'll still condense some of the time in spring and fall, but gas consumption is low in that period anyway.

    Of course the radiant zones will return cooler water. I was thinking only about the baseboard zones.
  • Floyd_16
    Floyd_16 Member Posts: 13
    Hey Chuckles.....

    Your forgetting ONE very important thing.....

    The baseboard is desgined to heat the building one the COLDEST day of the year. Now how many days is it going to be at or even near that cold???? Right, not many...sooooo the rest of the time the boiler can be chugging along at much cooler water temps. and condensating like a race horse......like my Ultra right now....50 something outside... running at 115 and keeping me nice and toasty...:-)

    Modulating AND condensing are both good!!! :-) Together they really do compliment each other. Oh yeah,..... don't forget to mix in the outdoor reset.... It's like icing on the cake!!!!

    Floyd
  • Chuckles_4
    Chuckles_4 Member Posts: 43


    > Your forgetting ONE very important

    > thing.....

    >

    > The baseboard is desgined to heat

    > the building one the COLDEST day of the year. Now

    > how many days is it going to be at or even near

    > that cold???? Right, not many...sooooo the rest


    You're forgeting something...I already said that!
  • Floyd_16
    Floyd_16 Member Posts: 13
    Sorry,.....

    You did say some of the time in spring and fall... I guess I would have put that as MOST of the time in spring and falll no matter what you got for baseboard if it is enough to heat on the coldest day of the year.
    Yes, you did mention it, but not nearly as strongly as I would have, and was looking for.... I overlooked that reference completely.......

    Again, Sorry

    Floyd
  • Tim_24
    Tim_24 Member Posts: 53
    High Temp vs Low Temp Efficiency

    for one brand of boiler with which I am the most familiar, the difference in AFUE is 5% on average across the line when comparing "standard" 180 deg supply 160 deg return, vs low temp operation (@110 hws 90 hwr). 98% vs 93% DOE AFUE. The "worst" is probably about 15 to 20% better than what you get now.
  • Gerry Ermer
    Gerry Ermer Member Posts: 4
    reset

    You can also add an outdoor reset control to your systm ( some boilers come with them ) which automatically lowers the boiler water temperature when the ambient ( outdoor ) temps rise. This would assure you get the maximum system efficiencies while still heating the home in cold weather.
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