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  1. #16

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    Quote Originally Posted by sjsmithjr View Post
    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.
    Nope, don't own a TK3... I have a Rinnai R75lsi. Could have "got by" with a 53 but was advised to "upsize"... so I did.
    "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

  2. #17
    Geologist sjsmithjr's Avatar
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    Nope, don't own a TK3... I have a Rinnai R75lsi. Could have "got by" with a 53 but was advised to "upsize"... so I did.
    That's right, must be Jakura that has a TK3. The Rinnai R75lsi can also deliver 6 GPM at 50F rise but maxes out a 7.5 GPM and a 35F rise. Was the recommendation for a 53 based on Rinnai's online "tankless assistant" that you referenced in another post? Seems to me it's recommendations are a bit undersized; I entered my zip code and one bathroom a got a recommendation for a unit that could handle a bath group and little more.

    Seems the advice you got to upsize was good. Where have I heard that recommendation before?
    Last edited by sjsmithjr; 02-16-2009 at 11:37 AM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  3. #18

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    Quote Originally Posted by sjsmithjr View Post
    That's right, must be Jakura that has a TK3. The Rinnai R75lsi can also deliver 6 GPM at 50F rise but maxes out a 7.5 GPM and a 35F rise. Was the recommendation for a 53 based on Rinnai's online "tankless assistant" that you referenced in another post? Seems to me it's recommendations are a bit undersized; I entered my zip code and one bathroom a got a recommendation for a unit that could handle a bath group and little more.

    Seems the advice you got to upsize was good. Where have I heard that recommendation before?

    My plumbing supply guy will not stock the R53 as he says they are undersized for most installs in the area I live in. His reasoning, why stock something that will give problems, refuse the sale.
    "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

  4. #19

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    Quote Originally Posted by sjsmithjr View Post
    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.


    The typical tank type water heater is sized at what 30 to 40 gallons? At your specified 7 gpm, you are going to run out of "hot" water after at most 4 or 5 minutes of use. What good is tank type of water heater?


    The water pressure in the home will also drop when 7 gpm is drawn through the water distribution system. Have you ever drawn 7 gpm and observed what happens on your own home system?
    Last edited by Ladiesman271; 02-16-2009 at 01:49 PM.

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  6. #21
    Geologist sjsmithjr's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    Have you ever drawn 7 gpm and observed what happens on your own home system?
    I observe exactly what I should in a properly designed system - nothing of significance. Your point.

    ...and you still seem to fail to understand the difference in a storage system and a demand system when it comes to sizing.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  7. #22

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    Quote Originally Posted by sjsmithjr View Post
    I observe exactly what I should in a properly designed system - nothing of significance. Your point.

    ...and you still seem to fail to understand the difference in a storage system and a demand system when it comes to sizing.

    Sure I do. You are just being a wise guy!

    Since the majority of gas tank type water heaters are installed in the 40 gallon size, maybe you should properly figure out the typical home hot water demand instead of overstating it. Heck, one or two short showers back to back and a 40 gallon tank heater is producing tepid water in most homes if your demand figures are accurate for the average size home.

    As a comparison, even with 40 degree incoming water temperature I can get over 120 GPH of 120 degree hot water out of my modest tankless unit (125,000 BTU maximum).

    Like Mr. Rat said a hundred times, if you have a high hot water demand lifestyle (AKA 4 to 5 bedrooms - 3 full baths - simultaneous showers required), then you need to size your system to meet the required simultaneous demand.


    You should also note what it says in the previously linked to Minnesota summary. You, 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.


    Copy of original Minnesota summary with typical flow rate chart:


    Last edited by Ladiesman271; 02-16-2009 at 04:56 PM.

  8. #23

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    Quote Originally Posted by SewerRatz View Post

    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.



    That may in fact be terrible advice. The larger units have a higher minimum flow rate and may turn off in the middle of "low flow" demand situations.

    I hope that you guys do not do HVAC installations!

  9. #24
    Geologist sjsmithjr's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    You are just being a wise guy!
    I can assure you I am not. The plumbing system in my home is neither undersized nor is it oversized. It is appropriate for it's intended demand I am not limited to as to simultaneous fixture use. My water heater is not oversized. My observations are not qualitative but quanitative.

    Tankless manufacturers recommend that units be sized for the coldest parts of the year, meaning that at least part of the time they are oversized.

    As you seem to take issue with the opinions most professionals regardless of field as well as qualified instructors, would you mind sharing your particular area of expertise and qualifications?

    Just curious.
    Last edited by sjsmithjr; 02-16-2009 at 06:04 PM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  10. #25

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    Quote Originally Posted by Redwood View Post
    The silence is deafening....


    It sure is!

  11. #26
    Geologist sjsmithjr's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    The larger units have a higher minimum flow rate and may turn off in the middle of "low flow" demand situations.
    Be specific; which residential units have this problem? What are their minimum flow rates in GPM for a given temperature rise? Even a Rinnai R98 works at 0.6 GPM/50F rise. Even if minimum flow were a problem, one could install two smaller units, albeit at a greater initial cost.
    Last edited by sjsmithjr; 02-16-2009 at 06:13 PM.
    -Sam Smith
    Licensed Professional Geologist - AL, TN, KY

  12. #27
    Master Plumber master plumber mark's Avatar
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    Talking its all smoke and mirrors....

    Quote Originally Posted by Ladiesman271 View Post
    Ladies man, you are truely an intellegent person
    and I stand in awe of all your knowledge....


    Why are beating a dead horse and having a fun time
    trying to pull everyones chain.. I dont understand...

    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......

    lets try to equate the flow rate when grandma takes
    a healthy shit and 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 stubborn nasty hard turd 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..?????

    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 damn simple for you.....

    isnt it???..

  13. #28
    Master Plumber Redwood's Avatar
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    Quote Originally Posted by Ladiesman271 View Post
    It sure is!
    Yea I was wondering when You were going to post the meaningful Data you were asked for...

    Slipped out of another one eh?
    Last edited by Redwood; 02-17-2009 at 11:42 PM.

  14. #29
    Master Plumber nhmaster's Avatar
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    flow rates and demand aside why not address the real folly of tankless heaters and that is that the average savings is a crappy 4% over conventional tank heaters with the installed price being 2 to 3 times that of a tank type heater. That's a lot of money to save very little floor space. Why not address the common problem of long wait times for the water to get to the faucet or how if you just crack a faucet the unit will not fire or how the temperature and pressure fluctuate enough to keep quite a few pressure balanced valves from operating correctly. better yet ask anyone from Europe that has grown up on these things what they think about tank type water heaters when they come over here for a visit?

  15. #30

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    Folks, here's what 15 or more pages of debate boil down too. Several (ie, more than 2) DIYers have installed tankless systems in their homes and are happy with them. Plumbers around the country are installing them successfully (ie. no manufacturer recalls). A few "boys" here hate them for highly biased reasons.

    Bottom line, don't let NHmaster install one in your home as he can't cope with it. And don't let Rugged in your home or you may be "scammed" out of a water heater that is under warranty.

    Now for more FUD (and dumb pictures) from the "boys".
    "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

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