40 amp 240v tankless to replace 40 gallon?

Discussion in 'Tankless Water Heater Forum' started by JerryR, May 29, 2015.

  1. JerryR

    JerryR Active Member

    Joined:
    Jul 27, 2011
    Location:
    Florida
    My brother-in -law was telling me that at his condo residents are having 40 amp tankless water heaters installed to replace aging 40 gallon tanks. It seems the electric service will not support anything larger.

    This is in South Florida where incoming water rarely gets below 70 degrees.

    Of course it wold require upgraded electric supply from breaker box. Seems they are being quoted $800 for the job.

    I told him I don't believe that a 40 amp tankless would handle a small 1400 sq ft 2 bedroom 2 bath as the sole heater.

    What do you think?
     
  2. BadgerBoilerMN

    BadgerBoilerMN Hydronic Heating Designer

    Joined:
    Mar 4, 2011
    Occupation:
    hydronic heating designer/contractor
    Location:
    Minneapolis
    I would not use a tankless electric water heater unless space was an issue. With the new energy code and upgraded insulation in a warm climate the standby losses from a tank water heater are very low. If I had to do it I would use a 28 kW (requiring 3-500 amp breakers) tankless electric in S. Florida and then only with soft water.
     
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    The way I calculate it, if everything was perfect, and it isn't, a 40A circuit should mean a 32A continuous load maximum to account for the 125% rules. 32A*240v=7680W or 26205BTU. Assuming 70-degree inlet water temp and a desired 110-degree outlet, that's about 1.3gpm. Hardly enough for even one shower. Now, get a brownout or say the middle of the winter with the voltage lower when everyone's heater is running and/or the water temperature down, and it could be even more dismal. IMHO, that size unit is okay for a single point of use for maybe a kitchen sink, but not much of anything more. Dont' even think about trying to fill a tub or washing machine with hot water. If it was a true 40A input device, then it would require a 50A breaker for the 125% rule (which I think applies, since it might end up running a long time), but it wouldn't be all that much better.

    Most tankless systems that are really worth much are gas, and they have around 200K btu, or nearly 8x what that electric one has.
     
  5. Kayleigh Bohannan

    Kayleigh Bohannan New Member

    Joined:
    Jun 16, 2015
    Location:
    South Carolina
    With the new DOE regulations that "Badger Boiler" mentioned, yes the tanks or becoming more efficient, but they are also becoming larger, louder and more expensive. Tankless would not only save you space but, if you purchase the Heatworks MODEL 1 electric tankless water heater, it would be silent and cost less. The MODEL 1 performs great, if not better, with hard water so worrying about how hard or soft the water is isn't an issue. It is roughly the size of a football and can be placed anywhere in your home, even under cabinets, freeing up the square footage you are already wasting on a tank (or saving you even MORE square footage once you replace it with a tank that meets the new standards). The Heatworks MODEL 1 retails for $475, however, you may need more than one depending on your GPM demand, your incoming water temperature and your desired temp rise. If you live in Florida, your incoming water temperature varies from 72 - 77 degrees. If you want your shower to be anywhere from 105 - 110 temp (105 is the average shower temp) that is only a 33 - 28 degree temp rise (if going with 105). Lets say you are taking one shower at a time (2 GPM average) then you would only need between 9.66 and 8.19 kW. Each MODEL 1 has a capacity of 12 kW. Now these results would be from running your Heatworks MODEL 1 at full power which is 48 amps and 250 volts (i would suggest either a 50 or 60 amp breaker dedicated to this). If you want to learn more and properly size for a MODEL 1 tankless electric water heater visit this site http://myheatworks.com/technology.php . In the interest of full discloser, i do work for the company that invented this product, however this could solve all your issues while saving you money on energy and water. JerryR, if you have any issues or questions, or any one on this forum for that matter, let me know and i will do my best to help you guys out. thanks!
     
  6. Dana

    Dana In the trades

    Joined:
    Jan 14, 2009
    Location:
    01609
    If and when rates are restructured with residential demand-charges to better reflect the grid infrastructure costs for supporting the loads, an electric tankless will start looking like an expensive luxury. Demand charges are already being considered in several US utilities as a way to guarantee that net-zero power use solar customers are paying for their "fair share" of the grid infrastructure once solar becomes ubiquitous and cheap. A demand charge is based on the absolute peak power draws over some minimum duration (an hour or half-hour is typical, but some are as short as 15 minutes), during a billing period. Spiky high-draw loads like electric tankless hot water heaters could become a real factor in a residential demand charge, since there are few other loads that bit.

    It's the peak power draws that determine how big and expensive the distribution grid components are, not the average. Peak draws are what ages that equipment too. Replacing a whole condo development's 40 gallon tanks with tankless units is a recipe for rapidly aging the transformers serving the building.
     
  7. WoodenTent

    WoodenTent New Member

    Joined:
    Dec 27, 2015
    Location:
    Earth
    In the near future everything will be electric and gas fired anything in a house will be outlawed as everyone realizes we can't keep burning stuff. Just requiring emission systems on water heaters/furnaces the same as cars have to comply would all but kill gas anything in a house. Electric grid is continually upgraded and made more efficient, more capacity and cleaner. Gas grid is not.

    Usage metering is fine, it will only cause a market for battery systems to grow. As is I could pay off a Tesla Power Wall battery with time of day metering years before the warranty expires just from cost savings using my tankless water heater. Electric Utilizes are not responding to change well as they have been able to work exactly the same for 100 years. Their greed will only cause more people to go solar, battery systems and off grid. If utilities would just accept something as simple as a fixed base fee for feed into the grid, or just lock in to something like paying customers 95% per kwh of what the customer pays per kwh to handle grid fees, they would be fine. But trying to stop feed in programs, or have horrible price structures will just cause people to go off grid, or grid zero with some energy storage.
     
  8. BadgerBoilerMN

    BadgerBoilerMN Hydronic Heating Designer

    Joined:
    Mar 4, 2011
    Occupation:
    hydronic heating designer/contractor
    Location:
    Minneapolis
    Hard water kills water heaters, period. My Rheem Marathon is silent and stores hot water using off-peak energy, saving me money and the utility (a co-op, no greed here) peak load anxiety. Same for my electric boiler and heat pump.

    If everything is electric we will still be burning fossil fuels to generate it for the foreseeable future. You still can't convert one energy to another and yet another, deliver it to your outlet and "save" anything.

    Utilities are responding like corporations (people organized legally to act as one) will. Generally, rationally and responsible to their share holders.

    When a tank-less water heater pays for a Tesla Power Wall, worrying about utility rates will be a moot point.

    http://www.greencarreports.com/news...y-save-money-cost-calculator-helps-you-decide

    Perhaps if they shut down all the coal-fired plants in the US, while China builds a new one every week, and our electric rates nearly triple to the German standard we can get "somewhere".

    http://instituteforenergyresearch.o...oal-plants-china-and-japan-are-building-them/
     
  9. DonL

    DonL Jack of all trades Master of one

    Joined:
    Mar 30, 2011
    Occupation:
    Rocket Scientist
    Location:
    Houston, TX
    When that happens, You will have more to be worried about than Hot water. :eek:
     
  10. BadgerBoilerMN

    BadgerBoilerMN Hydronic Heating Designer

    Joined:
    Mar 4, 2011
    Occupation:
    hydronic heating designer/contractor
    Location:
    Minneapolis
    Actually, we have to perform a combustion test on all of the gas boilers installed in Minneapolis or St. Paul. Our condensing boilers make the cleanest car look like a 1950's coal-fired plant with the lowest NOx and SOx anywhere, exceeding California standards since the mid-80s.
     
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