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DHW question?

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John@Reliable_4
John@Reliable_4 Member Posts: 101
in THE MAIN WALL

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  • Joh n Brickey
    Joh n Brickey Member Posts: 43
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    When sizing a boiler for heating and domestic hot water my rep told me to double the size of the boiler. I don't think I would have to if I use a priority type control any comments on this. Thanks!
  • ScottMP
    ScottMP Member Posts: 5,884
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    Sooo

    If you have a Boiler output of 170,000, you would then put in a 340,000 output boiler ?

    Wow good saleman.

    Scott

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  • Floyd_5
    Floyd_5 Member Posts: 418
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    Use a modulating boiler...

    then it can make DHW on priority and still have the balls to catch back up and then just purr away @ half thottle or so....
  • Joh n Brickey
    Joh n Brickey Member Posts: 43
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    These are great comments. I thought this was heating help not rip on the posters. All I asked was how you sized the boiler for DHW. If you can't post something worthwhile shut the hell up.
  • Floyd_5
    Floyd_5 Member Posts: 418
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    WOW!!!!!

    A little touchy... aren't we????
    I think what they were getting at is the ridiculous statement that was made by your rep.!!!!
    The fact is that DHW heating with priority is usually a non-issue with most any boiler that is sized to heat a typical house.
    As long as your puttin' out 80,000 or better you will have plenty to make hot water with.... I have seen little 40 or 50,000's work great, just takes a bit longer to recover.

    If you really want tons of hot water and have a small heat load, then consider a 2 stae or modualting boiler that will give you what you need when you need it. Oversizing your boiler is like having an 800HP motor in a NEON, she'll get you where you want to go real quick... but not very efficiently!!!!!

    Oh, and please cool down....no one is ripping you!!!!
    Just get tired of people that should know better giving out info designed more to make a buck, than to help people!!!

    Floyd
  • Joh n Brickey
    Joh n Brickey Member Posts: 43
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    Floyd, thank you very much for the straight answer. I shouldn't drink so much coffee this late at night. What my rep went by was a chart by Burnham. It was sort of silly to think that I would have to size the boiler so big. The house that I am doing has a 65,00 btu heat load and I am installing a Munchkin 85,000 btu boiler. With the priority control I would think this would be plenty to handle say, a 50 gallon DHW. Yes?
  • Floyd_5
    Floyd_5 Member Posts: 418
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    You will be fine....

    Unless you are installing one of the "car wash" showers or plan on running a bunch of hot water at once.. you should be in great shape even wth a 40 gal. DHW tank.

    Glad your calmed down a bit, hope you can sleep well now...:-)

    Floyd
  • ScottMP
    ScottMP Member Posts: 5,884
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    Sorry John

    My remark was aimed towards the rep. Would have been better had I given you Flyods answer also.

    Flyod is correct. I know alot of guys upsize the boiler for domestic output. I like to have at least 100,000 for recovery. A small project like yours with a munchkin will be fine. The munchkin will adjust to heating demands and temper its output accordingly.

    Make sure you size the tank for the volume you will need regardless of output. If you have a three showers and four daughters a 40 gallon tank won't do it. If you have a 68 gallon whirlpool then a 60 won't do it no matter what the input is .

    And by the way, watch out for that rep. That really is not good info.

    Scott

    To Learn More About This Contractor, Click Here to Visit Their Ad in "Find A Contractor"
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    Need to find a link again...

    Can't recall the manufacturer, but they had REALLY good info regarding indirects.

    "...designed to use the reserve capacity of the boiler when outdoor conditions don't require everything going to the space heating system..."

    "...will be inefficient if boiler is increased in size to accommodate the indirect or used only for an indirect..."

    Will try to look for it today and post the link.
  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928
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    One Link

    http://www.bockwaterheaters.com/technical/pdf/sizing_section1.pdf

    There was another but it was probably in another .pdf file and you can't search those by keywords...

    The relevant portion is on the 1st page under "Indirect Sizing". Appears to be a good source for sizing for hot water loads regardless...

    I first researched this when someone here posted photos of a residential system with a multi-boiler setup--one of which was essentially dedicated to DHW. It seemed strange then as well...

    As homes have become more efficient and baths more elaborate it seems to be more common that the DHW load exceeds that of space heating.

    Maybe I'm reading too much between the lines, but the idea of "sizing the boiler to the DHW" seems to me to amount to "dedicating the boiler to DHW production". If the questions/problems posed here at The Wall are a fair judgment of reality, doing so often results in problems in the space heating component.

    Also important in that link is the statement about "not relying on recovery for capacity". Perhaps its better to increase the storage capacity of the indirect instead of increasing the size of the boiler...

  • Joh n Brickey
    Joh n Brickey Member Posts: 43
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    Thanks everybody I am going to study this a bit more and thanks for the link to bock.
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