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Tankless water heaters

HeatingHelp Administrator Posts: 654
edited October 2018 in THE MAIN WALL

Tankless water heaters

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  • Jack
    Jack Member Posts: 1,047
    So, John, the next time you produce the "definitive analysis", you may want to come at it from a neutral position discussing the features and benefits of tankless vs tanks rather than slanting every point to your predisposed position of anti tankless.
  • jumper
    jumper Member Posts: 2,332
    Jack said:

    So, John, the next time you produce the "definitive analysis", you may want to come at it from a neutral position discussing the features and benefits of tankless vs tanks rather than slanting every point to your predisposed position of anti tankless.

  • DavidMarasow
    DavidMarasow Member Posts: 16
    So when DO YOU suggest to go tankless??
  • Joyia
    Joyia Member Posts: 1
    Dear John,

    I appreciate your shared thoughts.
    I'm just an engineer and researcher using field data to improve the products available to all of us to solve real world needs.
    (I am NOT a member of the industry and have NO financial interest in promoting any system.)

    It seems like your long experience of doing things a certain way is founding a bias preventing you from searching out factual comparison data; - as summed up in your statements: "They do a great job and lots of homes in Europe use them." & "They simply don’t provide hot water the way we Americans are used to having it." * (check out the footnote if you feel so inclined." )

    While you are bringing up some valid points of consideration, some of the numbers you cite and the arguments you are attempting to make with them simply are not in line with reality.

    - To make it easier for anyone interested, just like us, to figure out these problems incorporating the findings of the most 'independent' research there is, I am linking to THIS unbiased MN state study, which went to GREAT lengths to fairly compare different heater systems SIDE by SIDE in the VERY SAME HOMES:

    As to the exhaust question: Yes, you are right flue gasses must terminate away from any building opening such as a door or window. BUT, this is the same for any type of gas fired water heater - no matter if tank or tankless; - with the difference that modern condensing tankless heaters CAN terminate on the side of a house - as well as through a(n existing) roof vent, as much of the toxic gasses are condensed=liquefied and can be neutralized to wash down the drain, instead of posing a danger to filter back into the air you breathe through windows or doors; AND they are much more flexible as to what hey can use as a flue, - incl. low cost PVC -, as their exhaust temperature is that low.

    As to your statement about maximum BTU capacity of tank-type vs. tankless water heater: You are right that,
    for same household size and usage, you'll want a tankless water heater with a considerably larger maximum momentary intake capacity than your old tank-type heater. (199,000 BTU to replace a 50-75,000 BTU tank type are a safe estimate.)
    BUT claiming that
    "Your tankless heater will be on, probably burning 200,000 BTUs per hour for all of that time"

    - Modern TANKLESS water heaters are taking in BTUs dynamically, - only as much as needed to accomplish the job of heating JUST THE AMOUNT of water required at a time to JUST THE TEMPERATURE required, and therewith RARELY EVER operate at their max. capacity.

    - Whereas TANK water heaters take in their whole BTU capacity every time you empty them and spend MOST OF THEIR OPERATING TIME ON that max. input and all of the rest of their operating time in a very steep virtually linear 'curve' right around those max values.

    THAT is why a TANKLESS water heater will do the (not so) "same job" of 'heating the amount of water your household needs in a day to be available the moment you need it' at a lower average cost, - and that COST will DECREASE, THE MORE you USE.

    -> see figure 8, 2 & 1 in the above mentioned publication

    As to the supply capacity in gpm of any given tankless heater: Yes, you are right, that depends on the amount of degrees you want to raise your incoming water temperature. BUT, modern tankless heaters with a capacity of 199,000 BTU, as you cite, are capable of achieving much greater flow rates at the given temperature raises you cite (compare Takagi H3 or Bosh Greentherm with 9.5 gpm at a raise of 40 deg. F to 5.4 gpm at a raise of 70 deg. F).

    As to what you can power with that amount of maximum flow: Your statement of 1 shower consuming 4.5 gpm is WAY off.
    That's the amount a fully opened pipe lets into a washer. - Even rain-shower heads are no more than 2.5 gpm, whereas in many parts of the country it is illegal for any shower head to be sold with a flow over 1.7 gpm.
    With that, a flow rate of 5.4 gpm at a 70 deg F raise (- like from the 40s, as you cite, up to comfortable & safe 110s -) you can run 2 rain-showers -3 normal showers simultaneously, while still having flow capacity left to run an additional hot tap at the same time with zero flow restriction.

    I am glad to read that you are "dedicated to understanding and embracing new technology" in your field, I very much hope you will continue to make your invaluable field experience available to All in the field, while simultaneously checking that experience against newly emerging actual field data.

    Please don't get me wrong! - I am VERY THANKFUL for you picking my brain and wish ALL the very best to you!
    Plentiful blessings to you!


    * (- Ever thought about why "Europeans" are able to live at a higher standard of convenience than US Americans, not only 'nation-wide' but union-wide, while at the same time being provided rock-solid insurances for all the basic pillars of what we call a 'civilized life' ?)