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Thread: Electric Tankless water heater 80 AMPS

  1. #1

    Electric Tankless water heater 80 AMPS

    Just saw this on one of the big box store websites. They have an electric tank less water heater. Says it is 80 AMPS. If you have 100 Amp service in your Circuit Breaker Panel, and you have more than half of that used up, what do you need to do , if you want to go the tank less electric water heater route? When I read the specs on it, it makes me wonder how much electric that thing really uses and what the electric bill would be per month with that ! 27 KV it says on it.

  2. #2
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    Clarence

    I would look at a different energy source than electric. Propane, or Natural Gas. You have to convert to btu's to compare the three.
    That is a relatively small On Demand unit. Full spec would equal 92,000 BTU's. At 80 amps it would be 68,000 btu's. Gas On Demand Units for a whole house are upwards of 200,000 btu's.

    There are 92,000 btu's per gallon of propane.
    There are 1000 btu's of natural gas per cubic/ft.
    I don't know what your cost per KW/HR is where you are at. A kW/HR equals about 3400 btu's.

    To estimate your bill you would have to estimate how much time you think it would be running, multiply by 70,000 divide by 1000, and multiply by your electric rate. AT 12 cents per kw/HR, it would be about $8.50 for every hour it is on. A shower would cost you about $3.00.

    If you only have 100 amp service, you will probably be advised/made to upgrade it. Your panel will power it, but the unit by itself is big penalty against the total load.

    Bottom line is that I haven't seen an instance yet, other than small point of service units, where electric comes out on top, when the cost per use is computed.
    Last edited by Mike Cutler; 10-02-2017 at 3:22 PM.
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  3. #3
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    I've never seen electric on-demand, but the few people I know who have on-demand gas water heating (propane, I assume), have been happy with it.

  4. #4
    Mike C gave you some good numbers - thanks, Mike. I have a natural gas tankless water heater and I found that my gas bill went down after I installed it because I wasn't keeping 40 or 50 gallons of water hot all day long when I wasn't using it. I only heated water when I needed hot water.

    I can highly recommend a natural gas tankless water heater. They're a bit more expensive than a tank water heater and if you're converting from a tank to tankless there will be some installation costs - you have to run electricity (120V, very low amperage) to the tankless unit.

    If your electricity service is not reliable you might might not want tankless - no electricity, no hot water.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  5. #5
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    Quote Originally Posted by Mike Cutler View Post
    Clarence

    I would look at a different energy source than electric. Propane, or Natural Gas. You have to convert to btu's to compare the three.
    That is a relatively small On Demand unit. Full spec would equal 92,000 BTU's. At 80 amps it would be 68,000 btu's. Gas On Demand Units for a whole house are upwards of 200,000 btu's.

    There are 92,000 btu's per gallon of propane.
    There are 1000 btu's of natural gas per cubic/ft.
    I don't know what your cost per KW/HR is where you are at. A kW/HR equals about 13,000 btu's.

    To estimate your bill you would have to estimate how much time you think it would be running, multiply by 70,000 divide by 1000, and multiply by your electric rate. AT 12 cents per kw/HR, it would be about $8.50 for every hour it is on. A shower would cost you about $3.00.

    If you only have 100 amp service, you will probably be advised/made to upgrade it. Your panel will power it, but the unit by itself is big penalty against the total load.

    Bottom line is that I haven't seen an instance yet, other than small point of service units, where electric comes out on top, when the cost per use is computed.
    Its actually even worse, one kWH = 3412 BTU. By any measure, electricity is virtually always the most expensive energy source available to homeowners.

  6. #6
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    Quote Originally Posted by John Lanciani View Post
    Its actually even worse, one kWH = 3412 BTU. By any measure, electricity is virtually always the most expensive energy source available to homeowners.
    John

    Thank you.
    3412btu/kw/HR is correct.
    I just did the calc for a friend at work to convert from electric storage water heater to On Demand Gas. 13,000 was the approximate number of total BTU's/hr for his water heater at it's rated capacity. I think that's why I had that number stuck in my head.
    I think the estimate he got was about $3500.00 installed and inspected. He has 5 kids,a so with 7 people in the household, his pay back will be much quicker.

    It's kind funny, because they use efficiency as a marketing tool and an electric water heater essentially has an efficiency of 1( 100%). But man, you're going to pay for that extra 8%-16% of efficiency.
    "The first thing you need to know, will likely be the last thing you learn." (Unknown)

  7. #7
    I would ask for a demo to see what the actual power usage is. The 80 amp value listed is likely much higher than actual. I have 2 Harbor Freight 'green' dust collector blowers that are listed on their website as 7 amps/750 watts. My Killowatt shows one uses 370 watts, the other 385 watts, just over half the rated value. Found the same thing when our new AC unit was installed last year, it was using only 2/3 its rated amps.

    That said, if gas is easily available, that would be my preference too..
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  8. #8
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    I also believe that you will need good water for it to last awhile,so if you have city water maybe its better than having well water.At work I know the plumbers have to replace them after just couple yrs of use due to the water condition

  9. #9
    Coming from the off-grid community. The problem is on-demand electrics are cheap. All you need is a reasonably efficient heat exchanger and a large enough power source. 60-80 AMPS is minuscule for an electric on demand heater other than for one that will feed a single shower or single bathroom sink at a time. Its not uncommon for large electric on demand heaters to be in the hundreds of amps.

    I would agree with others that a different heat source is needed. That said, when you move away from the simplicity of electric, you move into the cost and complexity of a combustion unity like a nat gas or a propane unit. Much less expensive to run but way higher up front cost, (fuel source, fuel lines, higher unit cost, flue cost and installation, and so on.

    The only electric on demands that are worth while are for a small single bath or super small home which is on the grid and hence has access to very cheap electricity.

    We have one of these in our shop and it performs perfectly. If no one is here, it doesnt run.

  10. #10
    Quote Originally Posted by Carroll Courtney View Post
    I also believe that you will need good water for it to last awhile,so if you have city water maybe its better than having well water.At work I know the plumbers have to replace them after just couple yrs of use due to the water condition
    Around here, you have to flush the tankless water heaters with vinegar once a year to clean out all the mineral deposits. Requires a pump and some hoses - not very expensive. Here's a web page that explains how to flush a tankless water heater. I did this page for my wife so that if I kick off unexpectedly, she'll know what to do.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  11. #11
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    I'm a tankless water heater fan and have two of them in our home...powered by natural gas. Endless hot water truly is a beautiful thing. The electric versions do work...in many parts of the world they are "standard", if you will, but yes, they do draw a bit of current when in actual operation. Why? Because the energy is needed to get the necessary temperature rise in the water while it's flowing.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #12
    too bad water isn't magnetic

    --that said, is induction heating used in electric water heaters?
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  13. #13
    Quote Originally Posted by Kev Williams View Post
    too bad water isn't magnetic

    --that said, is induction heating used in electric water heaters?
    No, it's resistance heating.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  14. #14
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    Induction would be a solution to a non-existent problem. Induction burners transfer almost all of the electrical energy to the pot. Resistance burners loose a lot of energy that is not transferred to the pot. The electric elements in a water heater are completely surrounded by water so have near perfect efficiency.

  15. #15
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    I have used both while living in Germany.

    The primary bath used natural gas, and that thing would kick out an endless supply of scalding water no mater what.

    We added a shower in a location without gas so we installed the largest electric one we could (I cannot remember what that translates into), but, in the winter, it was not possible to take a hot shower. In the winter, the water coming into the house was very cold. My point is that you also need to understand the minimum temperature of the water that will enter the tank and the desired temperature when it leaves. Be absolutely certain that you understand that before you install one of these.

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