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    Undersized boiler (5 Posts)

  • Bobbyt Bobbyt @ 9:04 PM
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    Undersized boiler

    I am trying to prove whether my new boiler was adequately sized for my house. Installer has increased water temperature twice to where it is now at 200 degrees. From what I have read, this defeated the purpose of installing a high efficiency boiler. The unit is a Carrier BW9 100'000 BTU with a Triangle Tube indirect water heater. I have been told that to figure the heating load, add up the lineal feet of fin tube baseboard & multiply by 580. To me,that would only be correct if the baseboard was installed correctly. Is there a way for me to figure out heat requirements or should it be done by a professional?
  • Zman Zman @ 9:59 PM
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    Little more info.

    What is the footage of the house? What type of construction? What part of the country? How many feet of baseboard?
    Is this a new install or replacement boiler?
    Pictures of the boiler piping is always useful.
    A heat loss calculation is the definitive way to determine boiler size. There are many free online calculators. Check out Taco's flow pro university if you are looking for some free lessons.
    If you post the above info someone can tell you if you are close. In many cases the distribution piping is incorrect.This will lead the knucklehead installer to turn up the temp. Higher temps will cost you efficiency.2
    Carl
  • Rich Rich @ 11:35 PM
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    Existing lineal

    feet of baseboard is NO WAY to determine boiler size or to perform a heat loss.  Most baseboard on the market is putting out more than 580 per foot with 200* fluid also .   What exactly was happening that is making your knucklehead , sorry contractor turn up the temps .   You are correct that the higher temps you are running would negate the logic behind installing modulating condensing equipment .  Taco does have a basic heat loss program built into FloPro Designer on their site as stated above . That should give you an adequate number to work with , Ra Puriri is online for assistance most of the time .
    You didn't get what you didn't pay for and it will never be what you thought it would
    This post was edited by an admin on June 29, 2013 11:38 PM.
  • Chris Chris @ 10:02 AM
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    That Boiler

    Would fit 99% of applications for a 4,000 sqft house in a zero degree climate. Is it piped direct or primary secondary? Pics tell a thousand words.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • ColoradoDave ColoradoDave @ 12:23 AM
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    Baseboard output

    Slant Fin 30 baseboard outputs 610 btu's per linear foot at 180 deg in.  So estimating your baseboard OUTPUT at 600 per foot at 180deg in, would give you the capability of the baseboard.

    If your house isn't heating adequately at 200 degree supply temperature, it could be many different reasons.   1> not enough baseboard installed, 2> too much baseboard in each loop, 3> boiler is undersized, 4> dirty fin tubes on the baseboard, 5> not enough air flow for the baseboard to properly convect.

    A heat loss, even a rudimentary one, would be a good first step to telling you what the load of the house is, room by room.  Then, you could measure the baseboard in each room and use 580 or 600 per linear foot to determine if there is enough baseboard. 

    Get some specs for your baseboard and see what the temperature curves are for it's output.

    Your temperature drop on each loop should be 15-25 degrees F.  They won't all be the same, 20 is a good temp difference for baseboard.  If it's a lot more than that, you've got too much baseboard on each loop.

    Once you have that heat loss at your design load (coldest day), you can use the temperature curves for your baseboard to redo your heat load calculations on the warmest day you'd want heat (i.e., if a room needs 12000 btus at 0 deg outdoor, it might only need 2500 btus at 50 deg outdoor ~ DISCLAIMER: THESE NUMBERS WERE ARBITRARY IN MY EXAMPLE).  
    Recalculate the water temperature needed based on available baseboard to output that load and you can set your boiler setpoint for your outdoor reset to gain the higher efficiencies.

    Zman, Rich and Chris are ALL totally correct.  We'd need more info, a heat loss should always be done, and 100,000 btu boiler can heat many 4000sf homes depending on where you live. 
    I'm in .... wait for it... Colorado!!
    My 1972 968sf home has a heat loss of 58,000..... so 4,000sf would be pushing it for a 100,000btu boiler built before the late 80's early 90's....  maybe something in new construction would do well.

    Slant Fin 30 spec sheet http://slantfin.com/images/stories/Technical-Literature/ratings_fineline30_r.pdf
    Industry recognized design temperatures based on your city can be found http://www2.iccsafe.org/states/virginia/Plumbing/PDFs/Appendix%20D_Degree%20Day%20and%20Design%20Temperatures.pdf & http://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/Outdoor_Design_Conditions_508.pdf
    I usually design for an indoor temperature of 70... that's the way I was taught to do it, I'm not sure if it's an "industry standard" or not. 

    Avoid using a "rule of thumb"... some people will say XX btu/sf for radiant, YY for baseboard & ZZ for forced air..... but in two houses with the identical footprint will have two different heat loads if they were built with different matterials/insulation/infiltration values.  Heat Loss calc is the only right way to do it.
    This post was edited by an admin on July 13, 2013 12:29 AM.
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