(206) 949-5683, Top Rated Plumber, Seattle
Page 1 of 3 123 LastLast
Results 1 to 15 of 34

Thread: Need some data

  1. #1
    Geologist sjsmithjr's Avatar
    Join Date
    Dec 2005
    Location
    Knoxville, Tennessee
    Posts
    295

    Default Need some data

    In an effort to make a meaningfull contribution to the topic of sizing tankless water heaters, I'm working on compiling a typical GPM deliverable map (maximum capacity, single unit) for the contiguous United States based on 120F and average water supply temp. I'm using DOE's fixture demand values to get a reasonable idea of available simultaneous demand.

    I've looked at the supply demand curves readily available on the major manufacturers websites but, quite frankly, the scale is too coarse as to be of use. If anyone has ready access to supply demand curves, say plus or minus one-half gallon per degree rise, I'd appreciate it.

    Thanks,
    Last edited by sjsmithjr; 02-13-2009 at 03:07 PM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  2. #2
    Master Plumber Redwood's Avatar
    Join Date
    Dec 2007
    Location
    Connecticut
    Posts
    7,463

    Default

    The silence is deafening....

  3. #3
    Master Plumber master plumber mark's Avatar
    Join Date
    Feb 2005
    Location
    indianapolis indiana - land of the free, home of the brave....
    Posts
    4,243
    Blog Entries
    1

    Talking They make it up as they go......

    Quote Originally Posted by sjsmithjr View Post

    I've looked at the supply demand curves readily available on the major manufacturers websites but, quite frankly, the scale is too coarse as to be of use. If anyone has ready access to supply demand curves, say plus or minus one-half gallon per degree rise, I'd appreciate it.

    Thanks,

    the situation and scales you are looking for simply do not
    exist for accurately sizeing a tankless water heater...

    their are simply too many variables to factor in...

    with any normal plumbing system, usually when you ar not sure about something you normally just increase the size up a notch to cover any shortfalls...

    my atitude when doing a plumbing system, is I would rather be too large than too small to accomidate either the water system or drain lines.... and its a simple matter of
    just increaseing the size of the system a tad bit....

    but with the tankless you are trying to make it perfect to
    be both economical and efficient .....


    to put in a tankless, I would rather oversize one that I know will do the job without any complaints in every situation , rather than undersize one and know it will not
    work properly..

    pullling your hair out is all you are going to accomplish
    trying to size one up


    go big or stay home......

  4. #4
    Illinois Licensed Plumber SewerRatz's Avatar
    Join Date
    Nov 2008
    Location
    Chicago, IL
    Posts
    1,705

    Default

    I agree with Master Plumber Mark. The biggest variable is how a house hold of people use their plumbing system. Yes there are people out there that is happy with the ability to run fixture all day long and get hot water. by the way "Hot water" is defined by Illinois plumbing code to be 120 Degree Fahrenheit or hotter. That same house hold turns on more than one fixture the temperature now becomes "tempered water" which by Illinois code is defined as "Tempered Water": Water ranging in temperature from 85F to, but not including, 120F

    Now to use a gas fired tankless water heater to supply a whole house with hot water the system does need to be sized properly.. To do this a plumber needs to know how many fixtures in the home are capable of using hot water, and the flow rates of each fixture. Once the flow rate is determined, then you need to figure out the water incoming temperature, which will give us our desired temperature rise. here in Illinois its pretty much 50F so to get our 120F temp we need a 70F rise. so now we have our rise temperature and total flow rate we can select a properly sized unit or units for that home.

    This is where sizing it one size bigger comes in handy though to handle the unforeseen variables. Like water temp dropping down to 40F, or the home owner feels they they do not need to follow the code because its such an inconvenience, and it wouldn't hurt anyone if they remove the flow restrictors from their faucet, or shower. And please does of you that just got the urge to argue that no one would say that they do not need to follow the code, read other posts within this forum. I see that a whole lot. As well I had home owners ask me if I could remove these water restrictors which of course I tell them I can not.

    So as Master Plumber Mark has said it all depends on the variables, and once you figure it out make it one size bigger to handle the unforeseen variables.

  5. #5

  6. #6
    Illinois Licensed Plumber SewerRatz's Avatar
    Join Date
    Nov 2008
    Location
    Chicago, IL
    Posts
    1,705

    Default

    See the trouble is they do not take into account the variables. and assume that people have low flow faucets and shower heads. Just read my post about the variables. I really hate chewing my cabbage twice. http://www.terrylove.com/forums/showpost.php?p=185058&postcount=4

  7. #7
    Geologist sjsmithjr's Avatar
    Join Date
    Dec 2005
    Location
    Knoxville, Tennessee
    Posts
    295

    Default

    Quote Originally Posted by SewerRatz View Post
    To do this a plumber needs to know how many fixtures in the home are capable of using hot water, and the flow rates of each fixture. Once the flow rate is determined, then you need to figure out the water incoming temperature, which will give us our desired temperature rise. here in Illinois its pretty much 50F so to get our 120F temp we need a 70F rise. so now we have our rise temperature and total flow rate we can select a properly sized unit or units for that home.
    That was how I was going to approach it. I already have an isopach map of the average (so I've already introduced bias) incoming water temperatures for the United States; they range from 37F to 77F. Assuming a 120F output temp would then require a temperature rise of anywhere from 45F to 80F. It shouldn't be that hard then to determine to GPM deliverable by incoming temperature zone. From there you could get an idea of how many simultaneous fixtures you could supply base on typical fixture demand. (Most of don't have 0.5 GPM lav faucets in our houses). You also have make some assumptions regarding water pressure and the overall condition of the plumbing system.

    For example, a single Noritz 9.3 might deliver anywhere from 5GPM to 9GPM within the above incoming temperature range. Of course, on the consumer side of their website they tell you can a 9.3 can deliver "up to 11.1 GPM" with the 9.3 GPM rating almost as an after thought.

    Here's where it get's maddening. The gpm curves that I've seen are based on 105F output, the units come preset to a higher temp, and if you can find any information from a manufacturer regarding the "cold water sandwich" effect it'll be based on 120F. (If you dig enough, you will find that all manufacturers acknowledge temperature stabilization issues and for some the temp swing is dangerous to your health.) In other words, it's all apples, oranges, and pears. Add to that the many variables inherent to any installation as noted by Mark and SewerRatz and sizing these things properly is not a task for the faint hearted. I believe Mark noted some thime back that noted that if you really wanted to DIY a tankless correctly, you'd know more about you plumbing and plumbing codes than you ever really wanted to know.

    In the end, it's almost a moot point to even be discussing these things in terms of a DIY installation. Electric models don't even warrant consideration. Homeowners aren't supposed to be able to buy Bradford White. Noritz and Takagi are explicit that to get a warranty their products have to be installed an authorized licensed contractor or approved and qualified plumber or contractor according to pertinent federal, state and/or local regulations. To date I believe Jakura is the only DIY're that has acknowledged the warranty issue for homeowner installations. He also subjected his installation to inspection by the appropriate AHJ. His tankless experiment thread is probably about the best by a Homeowner/DIY'er.

    In the end that leaves the Bosch 2700ES (4 to 7GPM) as valid option for DIY'er looking for a whole house unit, but not too many people give that unit a thumps up.
    Last edited by sjsmithjr; 02-16-2009 at 07:24 AM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  8. #8

    Default

    Quote Originally Posted by SewerRatz View Post
    See the trouble is they do not take into account the variables. and assume that people have low flow faucets and shower heads. Just read my post about the variables. I really hate chewing my cabbage twice. http://www.terrylove.com/forums/showpost.php?p=185058&postcount=4


    There are two issues here.

    1. How to "properly"size a water heater based on normal hot water usage. All you have to know is the normal hot water usage.

    2. Code requirements for water heater sizing. Why don't you post the specific Illinois Code section that deals with this issue as you have for other issues?


    I have never seen any definitive Code requirement for water heater sizing. In Massachusetts it fits in the general term of "adequate". In addition, the Massachusetts Plumbing Code refers you to the Sanitary Code with regards to hot water. There is also a link to the MA Plumbing code at the bottom of the Sanitary Code page.

    Massachusetts State Sanitary Code


    "Hot Water Facilities"

    "Facilities for the heating of water must be provided (i.e. supplied and paid for) and kept in good working order by the owner. The owner must supply hot water in sufficient quantity and pressure to satisfy the normal use of all plumbing fixtures which generally require hot water to function properly. The temperature of the hot water is not to exceed 130 Fahrenheit (54 Celsius) nor fall below 110 Fahrenheit (43 Celsius). Under certain leases, an occupant may be required to provide the fuel for the heating of the water. [410.190]"





    Here is part of the State of Minnesota version of proper water heater sizing.

    "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."


    State of Minnesota Department of Commerce - Water_Heaters


    Regarding tank type water heaters, the size reference notes that for gas hot-water heaters, "the most common size
    natural gas water heater is 40 gallons". Just how long will "hot water" obtained from a 40 gallon tank water heater last with the simultaneous use of all water fixtures which generally require hot water to function properly?


    You should also note what it says in the Minnesota summary. The "plumbing instructor" and his "friends" should revisit the so called and undocumented simultaneous use requirement of "the code".


    Summary

    • When looking at a new water heater, be sure
    to compare the energy efficiency of different
    models by checking the Energy Guide label.
    Choose an EF of at least .64 for natural gas
    and propane, and an EF of at least .93 for
    electric.

    • Buy the smallest size you can. Don’t try to
    buy a water heater so you can shower, and
    wash clothes and dishes all at the same time
    without running out. Instead, plan your hot
    water use. This is especially important if you
    have a large family.


    • Locate the water heater as close as possible to
    where the largest volume of hot water is
    used. Since heat is constantly lost through hot
    water pipes, the shorter the pipe runs the
    lower the heat loss.

    • Insulate the water pipes and install heat traps
    if your water heater does not have one.

    • Take easy, low-cost or no-cost measures to
    avoid waste in using hot water.
    .
    Last edited by Ladiesman271; 02-16-2009 at 04:15 PM.

  9. #9

    Default

    Quote Originally Posted by sjsmithjr View Post
    That was how I was going to approach it. I already have an isopach map of the average (so I've already introduced bias) incoming water temperatures for the United States; they range from 37F to 77F. Assuming a 120F output temp would then require a temperature rise of anywhere from 45F to 80F. It shouldn't be that hard then to determine to GPM deliverable by incoming temperature zone. From there you could get an idea of how many simultaneous fixtures you could supply base on typical fixture demand. (Most of don't have 0.5 GPM lav faucets in our houses). You also have make some assumptions regarding water pressure and the overall condition of the plumbing system.


    I think that Mr. Rat says that you should determine usage first, then select your heater.


    For a trial run this weekend I did a load of laundry & ran the dishwasher at the same time. Along with the simultaneous use of those two units I ran the hot water fixture in the kitchen. I measured 120 degrees at the kitchen fixture with the fixture set to the all hot setting. I still have 42 degree cold water coming into the house!

    You may want to look at the minimum water pressure that is required for use with a tankless water heater. The more fixtures that you open (hot and cold) at the same time, the lower the water pressure goes.

    In order to minimize water pressure drop, my washing machine alternates between hot and cold water when in use. The "cold" wash / rinse setting runs tap cold water for 75% of the the fill time, and hot water for 25% of the fill time. There is no simultaneous use of hot and cold water for any temperature setting.

  10. #10

    Default

    We seem to be stuck on this idea that if one fixture is "on" in a house and getting 120 degree water from the tankless then if another fixture is turned on then the temp will go down and stay down. Not true! At least in the case of MY unit that is not true.

    When water flow is detected the burner adjusts the flame size (aka BTU) in order to get the desired temp on the output side based on the flow demand. No mixing of water is done to get the right output temp at the tankless unit, only burner temp is adjusted. If the unit is raising the temp of water from 50 to 120 degrees and is flowing 2 gpm using one fixture and another 2 gpm fixture is turned on then MY tankless unit will raise the BTU rate of the burner to maintain the 120 degree output. What am I missing here?

    I do agree that some degree of oversizing is needed. You don't install for "today" but rather for the "future" as is foreseeable.
    "Dude, we can fix that. My old man is a TV repairman, he's got the ultimate set of tools!" --Jeff Spicoli


    http://web.me.com/greg.saulsbury/ChosatongaSpeaks

  11. #11
    Geologist sjsmithjr's Avatar
    Join Date
    Dec 2005
    Location
    Knoxville, Tennessee
    Posts
    295

    Default

    If the unit is raising the temp of water from 50 to 120 degrees and is flowing 2 gpm using one fixture and another 2 gpm fixture is turned on then MY tankless unit will raise the BTU rate of the burner to maintain the 120 degree output. What am I missing here?
    Nothing. For your unit and your location you could even turn on a third fixture with a 2 GPM demand and, assuming the pressure drop isn't too much, handle the demand. After that, flow and pressure would drop off to what most would consider unacceptable levels.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  12. #12

    Default

    Quote Originally Posted by sjsmithjr View Post
    Nothing. For your unit and your location you could even turn on a third fixture with a 2 GPM demand and, assuming the pressure drop isn't too much, handle the demand. After that, flow and pressure would drop off to what most would consider unacceptable levels.


    The cold water feed pressure from the meter coming into the house is also simultaneously dropping off to "unacceptable" levels. Kind of hard to take a hot "high" pressure shower when simultaneous hot and cold water use is at high levels!

  13. #13
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    Location
    New England
    Posts
    21,376

    Default

    Quote Originally Posted by gregsauls View Post
    When water flow is detected the burner adjusts the flame size (aka BTU) in order to get the desired temp on the output side based on the flow demand. No mixing of water is done to get the right output temp at the tankless unit, only burner temp is adjusted. If the unit is raising the temp of water from 50 to 120 degrees and is flowing 2 gpm using one fixture and another 2 gpm fixture is turned on then MY tankless unit will raise the BTU rate of the burner to maintain the 120 degree output. What am I missing here?
    What you are missing is IF the demand is greater than the ability of the unit at its maximum BTU rating is exceeded, the temperature of the outgoing water will decrease. If you are within the limits of its capabilities, you should not, in a properly set up unit, notice. But, there is no magic here...it is an easily calculated situation to determine if you can get the volume required with the BTU input you have available. I don't care how much it can modulate the output, if there is not enough heat, it can't magically maintain the output - and, the response is not immediate. I might be fast, but not immediate; and, when exceeded, the temperature WILL drop, or, you'll experience a decrease in pressure as you exceed the flow restrictor (if present).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  14. #14

    Talking

    Quote Originally Posted by jadnashua View Post
    What you are missing is IF the demand is greater than the ability of the unit at its maximum BTU rating is exceeded, the temperature of the outgoing water will decrease. If you are within the limits of its capabilities, you should not, in a properly set up unit, notice. But, there is no magic here...it is an easily calculated situation to determine if you can get the volume required with the BTU input you have available. I don't care how much it can modulate the output, if there is not enough heat, it can't magically maintain the output - and, the response is not immediate. I might be fast, but not immediate; and, when exceeded, the temperature WILL drop, or, you'll experience a decrease in pressure as you exceed the flow restrictor (if present).

    I agree with all of this... so we are back to "right sizing" the unit in the first place, just as you would with HVAC, electrical circuits, etc...

    The one neat thing with some of the better tankless units is the ability to grow the system by adding another unit and have them communicate with one another. I do agree that "upsizing" will pay off tin the long run. We could have "gotten by" with the R53 but since the dealer didn't stock that size and the cost diff was only about $175 then "go big, or go home".
    "Dude, we can fix that. My old man is a TV repairman, he's got the ultimate set of tools!" --Jeff Spicoli


    http://web.me.com/greg.saulsbury/ChosatongaSpeaks

  15. #15
    Geologist sjsmithjr's Avatar
    Join Date
    Dec 2005
    Location
    Knoxville, Tennessee
    Posts
    295

    Default

    I submitted my reply before I was finished. Jadnashua has hit on the rest of "equation". Greg has a TK3 and, on average needs 50F rise to obtain 120F water. He can get 6 GPM at 50F but if he pushes it to 7 GPM he can only get a 40F rise and will experience maximum pressure drop.

    Install that same unit in North Dakota and it will give you, on a good day, 3 GPM at 85F rise. The end result will be the same 40F rise at 7GPM, but in this case that means no hot water to any fixture.

    Yes, it's all about proper sizing. I simply wished to illustrate in a simple way what proper sizing might actually mean because after reading numerous online reviews, it would seem that a lot of people buy first and size later. Possibly due to the hype and possibly becausing purchasing a water heater used to be a no brainer.
    Last edited by sjsmithjr; 02-16-2009 at 10:40 AM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •