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Thread: Help Sizing a Tankless Water Heater

  1. #31
    Geologist sjsmithjr's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    Here is part of the State of Minnesota version of proper water heater sizing.
    Your link isn't to any code requirment but is an energy guide. Care to share with the class what the State of Minnesota has to say about tankless water heaters in their energy guide? Here, I'll save you the trouble of cutting and pasting:

    "Another major drawback is capacity. A tankless heater typically provides 1-2 gallons of hot water a minute. You may find this adequate. However, you may not have enough hot water for more than one use at a time. Before installing a tankless water heater, make sure its capacity will be adequate for your needs."
    Last edited by sjsmithjr; 02-17-2009 at 04:21 AM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  2. #32
    Geologist sjsmithjr's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    Maybe you have trouble reading all of the words, or perhaps you have a problem with comprehension?
    Not at all, before we go any further, however, may I suggest you read the following re decorum
    .

    The Minnesota document referenced is dealing primarily with topic of energy conservation and makes recommendations for reducing energy demand. These recommendations may or may not be agreement with current best practice re sizing of water distribution systems nor is there any certainty that such recommendations will be in agreement with code requirements such as those promulgated by State of Massachesetts.

    If you are truly interested in sizing hot water demands, I would suggest that you obtain a copies of the American Society of Heating, Refrigeration, and Air Condition Engineers Applications Handbook, the International Plumbing Code (IPC), the Uniform Plumbing Code (UPC) and the American Society of Plumbing Engineers handbooks that deal with this topic. You will find that each of these use probability theory to account for the various unknowns, which has been briefly mentioned in this forum. Depending upon your background, you may find it beneficial receive some formal instruction on the topic as well.

    I'll be more than happy to have a discussion with you, but continuing to berate longstanding members while contributing little more than a series of incongruous statements, nonprofessional opinions, and weblinks does little to enhance your credibility on this or any other forum you participate in.
    Last edited by sjsmithjr; 02-17-2009 at 06:47 AM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  3. #33
    Master Plumber master plumber mark's Avatar
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    Talking you simply havent got a clue

    Quote Originally Posted by Ladiesman271 View Post
    The question is not how to "properly" size a water heater. The question is what is the minimum size required by "the codes" that apply to your area.

    codes are not written in concrete .....
    and are usually open to intrepretation

    Ladies man, you are truely an intellegent person
    and I think that I speak for everyone here ....

    we stand in awe of all your apparent knowledge....

    or at least your ability to find info on Google



    having a fun time
    trying to pull everyones chain.. I dont understand why......

    you are trying to make tankless something akin to
    space shuttle technology.....

    its simply a bathroom,
    and everyone of them in the USA is different ......

    get it???


    ok lets try to factor in all the variables....THAT ARE NOT IN THE CODE..

    lets try to equate the flow rate when grandma usesand flushes the toilet while you
    are showering with the tankless...


    Now lets factor in a well, and now lets factor in
    pressure balanced shower faucets....


    Now factor in grandmas bowel movement not going down
    all the way with one flush...and she flushes three times
    to get that to go down....


    then she jumps into the other shower and attempts to
    take a bath while you are in the other bathroom


    so whats the pressure drop going to be..?????

    how bout that flow rate through the tankless?????


    man I can see that curve drop in my mind right now..

    so whats going to happen to the guy showering if the tankless is undersized??? ....






    When a simpelton like me sells a water heater

    the first thing I ask is how many people are presently living in the home,
    and how old everyone is living in the home....

    if they have a few children about 9 years old....
    I KNOW that the demad will be going up in about two years .
    ..


    and I KNOW that the 40 gallon heater will not suffice.
    ..

    so we usually go one size larger for the varaible of

    larger increased demand when the childred become pre-teens in a few years

    so they buy a 50 gallon..





    Now all I state....

    if you are putting in a tankless, I simply suggest
    you oversize the unit for future issues and other variable factors....
    like grandma and pressure drops....



    but this is just too darn simple for you.....

    isnt it???..
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  4. #34
    Retired Defense Industry Engineer jadnashua's Avatar
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    Code is a MINIMUM standard, but that does not mean it is optimum for the way most people live. This is especially true if you look at those values they list for hot water. Also note that first hour draw and the size of the tank (assuming you have a tank) are not the same thing as it is heating as you are drawing water - may not keep up, but still it is extending the runtime. The code doesn't distinguish whether you are trying to fill a big soaking tub or take a shower with an eco, really low-flow showerhead. This all comes back to what do you expect out of the system.

    My tank is rated at something like 180-gallons first hour draw, and if I wanted to (and do) fill a large tub fast, others could shower at the same time without experiencing flow or temperature problems. With your low-flow showerheads, that's essentially contant use by three showers. Can't do that with a typical tankless install (can be done, but at significant expense and complexity). A tankless can be set up to work with a recirculation system, but it becomes even more complex - a tank is essentially a no-brainer to perform the same task. Since most vanity faucets are already quite low-flow, washing your hands with warm water at most anything below full flow is impossible with a tankless. Easy with a tank.

    So, tankless costs more to install, purchase, and maintain (most people never maintain their tank, and they still last years without problems), and saves a little on energy over a good tank. Tankless systems have their place, but the average American may not want to put up with their foibles or expense. If you do, fine. Climate and use patterns are the big enablers, and much of the US environment and users will have trouble adjusting to them.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  5. #35
    Retired Defense Industry Engineer jadnashua's Avatar
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    You didn't ask, but I have an indirect tank, and calling people names and insulting their intelligence is not getting you anywhere. I may have confused things, but I thought it was you talking about around 1 gpm heads, or at least around that hot. My 60-gallon tank is run at 140, tempered to 120, and has a decent sized boiler firing it. It 'wastes' so much energy that it drops the temp while 'stored' at the rate of maybe 0.5-degrees/hour or less, so even if the power was off for a day, I could still have hot water available...try that on your tankless.

    This is getting really old...as noted, tankless has both good points and bad. If you can live with the bad, and must have some of the good, then fine...but it is not, nor will it ever be the best solution for all, let alone many.

    As an aside, try getting tepid water out of the tap and put it into say a measuring cup at full blast...it's hard, and may be impossible with a tankless. Simple with a tank since you get hot water at any delivery rate. Try filling a large garden tub in the middle of winter in the northern parts of the US in anywhere near a reasonable time with a typical tankles, and it won't happen. Your results may differ, but I've run the numbers...you'd need a huge tankless or several in series. A tank works much better and it's cheaper.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #36
    Retired Defense Industry Engineer jadnashua's Avatar
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    As opposed to the norm, I like a long hot soak in my tub any day I have the time, regardless of the time of year, or the time of day...

    First hour starts with the tank hot, but no flow and the burner/heat exchanger not providing heat. Then, you start the flow and measure how much hot you can get before the temp drops below the test value.

    Some places require hotter water to things like dishwashers, and with a tempering valve after then tank, you can reliably get that, any time of the year, regardless of the incoming water temp...this is not feasible with a tankless.

    For most tankless systems, it gets quite complicated to run a recirculation system, otherwise, whenever the pump is running, your tankless will be too. Not very good for longevity or your budget.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #37
    Geologist sjsmithjr's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    That FHR method does not follow government certification standards for water heaters.
    Well, if you want to go down that road, Table 5-1 of the UPC doesn't follow federal gov't certfication standards either. Oh well; good thing "the code" is a minimum and common sense (also known as best practice) can prevail.

    As for the several paragraphs of advertising copy from a particular mechanical contractor's website. What's up with that?

    FWIW I'm kinda hurt that I gave you the answer you were looking for re minimum water heater size based on "the code" and you never said "thanks".
    Last edited by sjsmithjr; 02-19-2009 at 05:13 PM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

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