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Radiant Boiler Sizing Choice

I was on the verge of purchasing the Triangle Tube Solo 60 when the Veissmann Vitodens 100 was recommended to me by a professional.  My entire heat load calculation totaled out at appoximately 33,000 BTUH.  I can't quite wrap my head around why I would need a boiler 3x larger than my heat load calculations, especially when the Vitodens only modulates down to 37,000 BTUH.  Wouldn't it be constantly short cycling even when modulating as low as possible?  Wouldn't the 60 MBH triangle tube or similr boiler that modulates down to 16 MBH be a better choice?   


  • CMadatMe
    CMadatMe Member Posts: 3,086
    I also questioned

    the 37k min on the boiler. This is the anwser I recevied from Viessmann on this.

    Once you begin to get lower than 25% of the rated output of a mod/con it tends to be tricky to keep the flame clean and maintain optimum efficiency. It also becomes tricky as gas pressures and quality change from the street and even harder with LP  to keep the flame clean and maintain optimum efficiency.  Remind you this only applies to the Vitodens 100 not the 200.

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  • NRT_Rob
    NRT_Rob Member Posts: 1,013

    lower minimum modulation is better. definitely. no question.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Radman
    Radman Member Posts: 75
    That is true on the 200 as well

    It is a major disappointment, but the new 200 only modulates to 8Kw unlike the old one that mods to 6.   Stick with the TT 60, you will be better off.  Set the parameters for continuous circ on ODR, and use modulating zone valves or TRVs.  I am a Viessmann dealer, but for small applications the new 100 & 200 don't quite cut it.  The offer the 4-11 in Europe, which would be sweet here in the US for more than 50% of the types of homes we do.  I don't know why they don't offer it,  and the response I get is that the market is too small for that boiler.   I can't think of a single house that I have heated with a load calc over 50K in the past 5 years.   That includes a couple of 6000 sf monsters.

    We'll get there...

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  • SpeyFitter
    SpeyFitter Member Posts: 422
    Go with the TT60 or the Lochinvar WB050

    I'd go with the 16-60 (16,000 to 60,000) Triange Tube or the 10-50 (10,000 to 50,000) Lochinvar WB-050 . Also, IBC (Vancouver) makes a 15-150 (15,000 to 150,000) if you have big domestic hot water demands or some light snow melt/pool/spa that could use the extra capacity of this boiler.

    It is too bad that more manufacturers can't get on the small mod-con or at least lower modulation bandwagon.  I'd love to see a mod-con that modulates to say 5000 to 8000 BTUH fires at 30,000 to 40,000 BTUH Max.

    There are more and more oppurtunities for these small boilers as heating systems become more sophisticated. For example, perhaps someone just has a space heating load in a more moderate climate (e.g. West Coast) and an electric HWT already, or a solar HOT water tank and they just need a little boiler back up or "top up" once and a while when the solar isn't as productive? How about a geothermal system that needs a little injection of boiler water on those extremely cold days to heat the radiant floors?  Also not everyone owns a 6000+ square foot house.

    Also, as building envelopes get tighter and people start to buid more efficiently this further may help demand for smaller modulating condensing boilers. And as heating contractors become more educated and start to do more realistic heat loss calculations, they too may start using these set ups.

    In homes that may suffice with smaller space heating loads but want some reasonable domestic demand you can buffer the smaller boiler with a larger indirect hot water tank as well.

    When you consider that most homes in more moderate climates rarely spend their time anywhere near design, but spend a significant time in the shoulder season, it'd be nice to see more of these gems out there.

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This discussion has been closed.