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  1. #1

    Seeking opinions on boiler options and sizing

    Hi all.

    First, thanks for this forum. I've learned a lot by doing some homework here.

    I have bids to replace our ancient oil-fired boiler and tankless coil (natural gas is not available here.)

    1100 square foot house on Cape Cod, with one bath, four people at most, and recently completed air sealing and insulation through the Mass Save/Cape Light Compact program.

    I did my own heat loss calculation using the slant fin calculator and came up with 28,600.

    Contractor #1 sized the boiler using the radiators, and is suggesting:
    1: Burnham MPO-IQ 115 with IQ
    2: Buderus 115 WS/4 w logamatic

    Contractor #2 did a heat loss calculation, and come up with 30,000 and suggests:

    Slant Fin Ec-13; no outdoor reset

    Contractor #3 sized using the radiators, and is suggesting:

    Buderus 115 WS/4 @ with logamatic (as did contractor #1, at a different price)

    All have offered indirect dhw options, which ill get to after I figure out the boiler (if that makes sense.). I'm planning on a 40 or 45 gallon.

    Question 1: aren't all of these options these oversized?
    Question 2: would these boilers require a chimney liner? (Contractor #2 mentioned this. I thought this was an issue with condensing boilers, but not these types/models?)

    What do you all think of these options? Any advice, suggestions for additional homework/research, etc?

    Last edited by BillCape; 03-07-2013 at 10:01 PM. Reason: Removing pricing info

  2. #2
    Join Date
    Jan 2012
    Broomall, PA
    IMO, all 3 boilers are nice, but all are way oversized. Also under the new laws in effect, new boilers are required to have some sort reset capability.
    A chimney liner is probably a good idea. If you don't go with a liner, you really should have a professional chimney co examine the chimney to certify its fine. You could also go with a direct vent on almost any boiler, and forego all the chimney questions.
    Burnham has a 84 MPO, would be better then the 115. I have the 115 in my house, for a 78000btu heat loss, with an indirect, and its oversized
    If I were you I would keep researching for the smallest boiler you can find.
    There are also condensing oil boilers, too.
    If you go with propane, you'll be able to go with a number of condensing boilers

  3. #3
    Join Date
    Nov 2011
    Long Island, NY
    With that heat loss go with the smallest boiler you can find. I have a G115/3 in a 2000 sq ft house on Long Island with a greater heat loss than yours and it's plenty big. Real outdoor reset controls help to compensate with a boiler that is over sized, which in your case can't be avoided. The Logamatic would be a good choice. The chimney liner is probably not a bad idea in this application.

  4. #4
    Join Date
    Nov 2004
    SW FL
    SLANT FIN SPECS attached.
    I don't know where you'll find a really small boiler.

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  5. #5
    Join Date
    Aug 2012
    North Dakota
    try to get away from oil

  6. #6
    Join Date
    Jun 2007
    Minneapolis, MN
    We specialize in designing HVAC systems for small homes, additions, basements and walk-outs. You want to heat space and hot water at once. Most of the time, in most markets a tank-type water heater will fill the largest tub and have the thermal mass required to serve the smallest micro-zone or small living space without short-cycling (death to combustion efficiency regardless of fuel or appliance).

  7. #7
    Join Date
    Jan 2009
    Keokuk, IA
    Badger, What tankless QH brands do you use the most? I know Rannai, Rheem, Bosch and Navien all haev approved use of their units. RHeem and Rannia market their own air handlers. First company has AHRI certification for their air handlers so you can pair it with a heat pump and go dual fuel. Hydronic and dual fuel is nice because you can ru nthe heat pump down to minimum temp while running aux at the same time. That way too, you still have soem heat while the tankless switches to domestic.... unless it's defrosting.... but a small amount of storage would resolve that issue, and also allow the use of recirculation.

  8. #8
    Join Date
    Jun 2007
    Minneapolis, MN
    We have used most of the tank-less water heaters available, Eternal being the latest, but do to the large outputs required for most DHW loads, find them a poor match for most of our small load hydronic systems. and high minimum fired rates. They are a better match for some fan-coil applications as you suggest.

    We fix a lot of under-performing combi-systems mis-matching otherwise good tank-less water heaters to low-load radiation. Tank-less water heaters have minimum flow rates, minimum return water temperatures and lack outdoor reset, something we can easily add to the plainest atmospheric water heater and likely have more comfort.

    We would like to use a condensing water heater with plate HX and ODR sub-assembly on most of these small loads where DHW is needed as well.

  9. #9
    Join Date
    Jun 2010
    Philadelphia PA
    I did my own heat loss calculation using the slant fin calculator and came up with 28,600.
    Me thinks that the contractors are not agreeing with your calcs. Question is Why didn't they do their own?
    You have got to learn from other people's mistakes! Because God knows you don't live long enough to make them all yourself !!!!!!!!

  10. #10
    Join Date
    Jul 2000
    Northern Wisconsin
    If you don't have the option of LP gas then your options are extremely limited. The heat load you've calculated is for worst case outdoor temperatures and that means that anything warmer than that and the short cycling of the boiler will only get worse.

    The first choice would be a LP modulating boiler.

    The second choice would be an electric boiler. I only suggest this because when you factor in installed, operational and maintenance of the oil boiler option I suspect the cost to heat with electricity might be a wash.

    The third would be an air to electric heat pump with electric boiler backup.

    The forth would be an oil boiler with some kind of buffering/storage to keep the short cycles to a minimum during the milder weather.
    Use the biggest hammer you like, pounding a square peg into a round hole does not equal a proper fit.

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