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boiler size?

wrxz24
wrxz24 Member Posts: 301
I am considering switching out our 7yr old 125k btu cast iron propane boiler w/ indirect dhw to a buderus gb142 wall hung.  However, I am not sure on which one.  My heat loss falls between two of the models as one would be slightly undersized and the other oversized. 



I did two heat loss calculations I found online and one was 76,000btu/hr  and the other was 93,000 btu/hr (I double and tripled check my numbers and can't find the difference) for a total of 4700 sq/ft of heated space (house and garage) 2 floors on heated slab and baseboard upstairs.

House sqft is 3500 and garage with bonus room is another 1200 sqft.  House is 8yrs old and well insulated.  Slab has 2 inch blueboard down and perimeter  4ft frost walls. 



So I guess my actual heat loss is going to fall somewhere between those two calculations. 



I know, the boiler I have now is oversized and I don't want to make that mistake again.  So my question is, Could I get away with using the gb142/30 even though it might be a little undersized when you factor in the DHW?



Thanks in advance.
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Comments

  • kcopp
    kcopp Member Posts: 4,092
    don't factor..........

    in the Indirect. Prioritize the HW and you will be fine.
  • wrxz24
    wrxz24 Member Posts: 301
    Thanks

    So if I already have a 50 gal indirect, should i use that as a storage tank for my hw needs?



    And I will be o.k with a slightly undersized bolier?
  • Zman
    Zman Member Posts: 7,434
    Gb 142 30

    If you derate your old boiler you will see is has an output of about 100,000 btu (assuming you are at sea level) The GB142/30 has an output of 91,500. If you prioritize the DHW, I would estimate you will have more DHW production with the GB142/30 than you do now. Given the Mod/cons ability to modulate and provide outdoor reset, your efficiency will be greatly improved.

    I know you did not ask. Why the Buderous? The aluminum block has proven to be problematic and Buderous has been less than responsive in addressing the issues with these boilers. I also don't understand why so many installers are still favoring the old horizontal coil boilers made famous by the munchkin. Google "triangle tube boilers problems" and notice how few hits there are.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • wrxz24
    wrxz24 Member Posts: 301
    why buderus?

    That is what the plumber install. Should I stay away from that mod/con?  
  • Zman
    Zman Member Posts: 7,434
    Opinions vary

    The aluminum exchanger in that boiler has proven to be a problem in The Rockys. It may be that the water is reacting poorly with the aluminum or perhaps they were being installed in applications with non O2 barrier tubing, I am not sure.

    I my opinion there are 3 major types of mod/cons. The buderus and a couple others have aluminum exchangers. The most common is the stainless horizontal coil that we first saw in the HTP "munchkin". These require regular cleaning and due to there high head loss characteristics, require bigger circulators and seem to have more issues with system pressure(many are installer related). The third is the stainless firetube. Triangle Tube made this design popular. Lochivar, Dunkirk and others have followed suit. I like these because they require less cleaning, use smaller circulators, and have a bit more water mass (less short cycles). As you research boilers you will find they fall into one of these categories

    I think it is important to find a boiler that your local tradesman carry parts for are comfortable with.

    Opinions will vary!
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • wrxz24
    wrxz24 Member Posts: 301
    short cycling?

    I certainly do not want that.  So, would I be better off looking for a boiler that has a SS exchanger?
  • Paul48
    Paul48 Member Posts: 4,469
    Simple Answer

    YES.......Flue gas condensate is acidic. The better choice for the heat exchanger is stainless steel.
  • wrxz24
    wrxz24 Member Posts: 301
    so,

    any recommendations for a mod/con boiler used for both in slab radiant and baseboard? 
  • Zman
    Zman Member Posts: 7,434
    Baseboard?

    How much baseboard do you have?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • wrxz24
    wrxz24 Member Posts: 301
    upstairs

    I have 68 feet in a 1400 sqft area plus and additional zone in the bonus room of 24 feet.  Downstairs is all in slab radiant with 2 zones.  No basement, 
  • Zman
    Zman Member Posts: 7,434
    Hmm

    How are your slabs controlled now? Ideally you would run those slabs on a reset curve that would range from say 95-120 degrees. Your baseboards will likely need a curve more like 110-150 degrees. Triangle's new controller can run 2 curves, it will always use the hotter if both loads are calling.This would be the most affordable way to do it.

    Tekmar makes controls that will either mix the floors down or cycle the zone valves to keep the "average " floor temp down. If you set it up right you could try controlling it with the TT and if you overheat the floors you could add the tekmar.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Paul48
    Paul48 Member Posts: 4,469
    ?

    I don't think any comfort would be sacrificed if the radiant waited until the baseboards were satisfied, and it could be done a lot cheaper than with tekmar.Simple controls instead of stacking technology.
  • Zman
    Zman Member Posts: 7,434
    Plan B

    Paul,

    I agree. The Tekmar should be "Plan B".

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • wrxz24
    wrxz24 Member Posts: 301
    mixing valves

    Controlled manually.  IF its cold , I jack up to 110 or 120 and if it isn't around 90 ish.  Bolier set at 180.
  • wrxz24
    wrxz24 Member Posts: 301
    Cheaper?

    Paul, I like the sounds of that.  Unfortunately, I have to replace this CI Smith gv100 boiler that is relatively new. So what it is a good bolier.  I have heard that TT is good as well as the Lochinvar.  Anyone know anything about Rinnai as that is one that my plumber recommends other than the Boderus?
  • Paul48
    Paul48 Member Posts: 4,469
    Two

    reset curves with priority control is even easier. Unless you can train the dog to adjust the mixing valves :)
  • wrxz24
    wrxz24 Member Posts: 301
    this dog

    forgets a lot of the time. :) What brands offer the 2 reset curve programming? I think I have it narrowed down to the Lochnivar and TT and maybe the Rinnai which all have the SS exchanger but not sure about the 2 curve reset.
  • Zman
    Zman Member Posts: 7,434
    Dogs

    Lochinvar now makes a firetube and a coil type exchanger. The rinnia appears to be cast aluminum. TT used to make mixing valve adapter for the older controller. It would be worth a call. I have never seen it in any literature, I have installed one.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Paul48
    Paul48 Member Posts: 4,469
    Carl

    Didn't you say TT new controller can run 2 reset curves?
  • Paul48
    Paul48 Member Posts: 4,469
    Gotta Love It

    I was looking at a manual for the Ultra, and it says because the HX is aluminum you have to make sure the ph of the water is between 7 and 8.5. How about the condensate on the outside that's 4 or 5?
  • wrxz24
    wrxz24 Member Posts: 301
    rinnai E110C

    has the ss exchanger.
  • Paul48
    Paul48 Member Posts: 4,469
    ?

    Combi-boiler?
  • wrxz24
    wrxz24 Member Posts: 301
    yes

    I guess it is.  
  • kcopp
    kcopp Member Posts: 4,092
    That Rinnai boiler....

    is available as a combi or a heat only.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited March 2012
    Boiler 2 Curves

    Viessmann Vitodens 200 WB2B-26 with a Viessmann mixing package will run 2 curves or as we call it 2 heating circuits while giving you DHW priority. HX is also 316 Ti Stainless with a lifetime warranty.



    http://www.viessmann-us.com/en/products/gas-brennwertkessel/vitodens200.html
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • CMadatMe
    CMadatMe Member Posts: 3,086
    TT Curves

    The new control can run 2 curves but you still will bleed the lower temp curve with the other curves hotter water. The control does not operate a mixing vlv or injection pump it can just run 2 zones at different curves.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Paul48
    Paul48 Member Posts: 4,469
    There's

    an idea......check out the price of that boiler and installation kit. I'll stand by with the smelling salts.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Unfair Statement

    Since we can't discuss price your statement is defensless. I can tell you that the WB2B-26 is competatively priced compared to other mod/cons in its size. None of the others mentioned carry the hx warranty nor do they use Lamda Pro combustion. Being able to plug and play a mix utilizing the on board control without having to out source others provides a nice clean system package that is easily wired and programmed.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Paul48
    Paul48 Member Posts: 4,469
    No

    need to defend it. If he does his homework, it will stand or fall, based on it's own merits and competiveness.
  • wrxz24
    wrxz24 Member Posts: 301
    I'm in Central Vermont

    so I am some what limited on a boiler in terms of local reps etc.  My plumber called one of his buddies in NJ about the Triangle Tube and there is a local rep so that is an option.  He doesn't know of any local reps for the Viessmann or Lochnivar.  He likes the Rinniai that offers both combi and heat only boliers.  I am leaning towards the TT but not quite sure which one?  Like I said, heat loss around 90,000 btu/hr.
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Viessmann Rep

    Hydronic Alternatives in Springfield MA is the rep and your in the heart of Viessmann territory.



    www.hydronicalternatives.com
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Paul48
    Paul48 Member Posts: 4,469
    edited March 2012
    Chris

    Can you steer him at a more appropriately sized boiler from Veissman?
  • CMadatMe
    CMadatMe Member Posts: 3,086
    I Think

    I did - WB2B26 is 31,000-93,000
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Paul48
    Paul48 Member Posts: 4,469
    My apologies

    In my original search for the boiler you were posting about, something very more expensive came up (twice the price).  What kind of safeties are in place to prevent the Lambda Pro combustion system from changing the selected gas type in case of a failure? There has been recent postings here on the "Wall" depicting the results of improperly converted gas burners and the scary results.
  • wrxz24
    wrxz24 Member Posts: 301
    Thanks fellas

    Both units look really good to me.  Tough decision that's for sure.  My house has 5 zones including heated garage and bonus room which the t-stat will be set much lower than the rest of the house.  Downstairs will be set for 70 which is a heated slab.  The upstairs  is baseboard and will require hotter water and with the set-up I have now, the upstairs baseboard calls for heat much less than the heated slab zones so my question is this, is there a way to control the boiler high temp when just the slab zones are calling for heat. Is that what having the 2 curve set-up can do for me? And since historically, there are only a few days out of the year when all zones are running at once, I can get away with a unit that is on the lower end of my heat loss calculations?  Thanks for your help and recommendations. 
  • Paul48
    Paul48 Member Posts: 4,469
    The

    2 curves would work for that, The Viessman seems to work with a controlled mixing which would take the place of the "Dog". With mod/cons you have to get away from the thinking "Bigger is Better". With any of the heat-loss calculations you might do, there is considerable play in the numbers. If you look around the "Wall", you will find countless postings from folks that were talked into up-sizing by installers that didn't understand mod/cons, didn't do heat-losses and installed the unit incorrectly.Think small, size it correctly, and install it exactly to manufacturers specification (not the installers interpretation).That should appear in the contract also.
  • wrxz24
    wrxz24 Member Posts: 301
    and the TT?

    How does their 2 curve system work?  Would I still utilize the mixing valves I have now? or would they not be needed? 
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Lamd Pro

    Doesn't change gas type. It monitors and optimizes combustion. Think of it as if you left your combustion analyzer in the flue and contiunally monitored and made adjustments on every start up and during every burn.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • CMadatMe
    CMadatMe Member Posts: 3,086
    Zone reset

    You basically have zone reset.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
This discussion has been closed.