load demand for new water heater

Discussion in 'Electrical Forum discussion & Blog' started by hammerslammer, Oct 27, 2007.

  1. hammerslammer

    hammerslammer New Member

    Messages:
    68
    Location:
    Colorado
    I'm down to the wire on getting my 4- plex lowboy gas water heaters switched to 50 gallon electric and I'm checking the load calculations one more time. I can't seem to find the online calculator i used in the past and the mike holt calculator shows a 100 amp serv no matter what i put in.

    Here is what I have. 90 amp main in each unit. 1100 sq ft. each unit with Electric range, Dryer, Fridge, DW, disposal. Heat is gas furnace and there is no AC. The last time i ran the calcs adding an electric water heater was no problem but I would like to confirm that.

    Thanks for all the great help on this forum. HS
  2. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    230.79(C) One-Family Dwelling. For a one-family dwelling, the service disconnecting means shall have a rating of not less than 100 amperes, 3-wire.
  3. hammerslammer

    hammerslammer New Member

    Messages:
    68
    Location:
    Colorado
    Thanks, this is an existing 90 amp. built to code in 1985. Does that make a difference??
  4. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    I don't get what the question is. Is there one?
  5. hammerslammer

    hammerslammer New Member

    Messages:
    68
    Location:
    Colorado
    Yes, i need to put an electric water heater in and take out the gas water heater. Do I have enough juice??
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,815
    Location:
    Cave Creek, Arizona
    heater

    You haven't told use the element wattage of the heater(s). If they are resiential units with 4500 watt, non simultaneous operation then the draw is approximately 20 amps with a 30 amp breaker.
  7. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    Even that, at 1100ft/sq you should be fine, especially considering no A/C.
  8. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I don't know if the 90 amp service is adequate. But I wonder why you are switching the WH from gas to electric?? In most areas, it seems that it costs a lot less to run a gas unit.
  9. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    The wording of this section is the same today as it was in the 1984 code cycle.
  10. hammerslammer

    hammerslammer New Member

    Messages:
    68
    Location:
    Colorado
    Thanks Pete. That's what i needed to know. I got a little tongue tied describing.

    Thanks Jim. I have lowboy gas, the ones they don't make anymore. Even at that they were dug into a hole in the crawler and i couldn't get them to pass today anyway. So I'm comming out of the crawler and can't seem to work out anything is gas so I'll put these electrics in and maybe in 6 years I'll have more options... Our gas doubled and electric stayed at about 7.5 cents so I think I'll be alright for a few years.

    Thanks JW,

    I don't know but I know I was there when all the inspections was done in 1985 and generally speaking our requirement have always been fairly strict. That's why I'm trying to keep my ducks in line. I can anticipate an inspector who might say " Bring the whole building up to current code" because i'm changing a water heater.
  11. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    At 7½ cents per kwh for electric, an electrice WH is not a bad choice. Our electric is 16 cents!
  12. Speedy Petey

    Speedy Petey Licensed Electrical Contractor

    Messages:
    996
    Location:
    NY State, USA
    7.5 cents???????????? :mad:
  13. hammerslammer

    hammerslammer New Member

    Messages:
    68
    Location:
    Colorado
    Actually 6.9 cents but there is the 22 cent per day access so I figure a little more. That is about what it was in 1985. Hope they can hold out for a few more years... Our gas is 60 cents per ccf with a 30 cent per day access. That is about double from 2 years ago.
  14. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,540
    Location:
    North Carolina
    1100 sq ft. each unit with Electric range, Dryer, Fridge, DW, disposal. Heat is gas furnace and there is no AC.

    1100 x 3 = 3300
    Small appliance and laundry 4500
    Range 12,000
    Dryer 5000
    Fridge is included in the small appliance circuits
    Dish washer 1200
    Disposal 750
    Total 26,759

    First 10,000 at 100%

    16750 x 40% = 6700

    6700 + 10,000 = 16,700

    16,700/240 = 69.58

    Now lets add a water heater = 77.09

    Change the 90 amp breaker to 100 and be done with the job.
    Make sure that the SE cable is either #4 copper or #2 aluminum
  15. hammerslammer

    hammerslammer New Member

    Messages:
    68
    Location:
    Colorado
    Thanks JW. I got the breaker changed out and every thing done and inspected today. Went pretty smooth and I'm happy to get one appliance out of the crawler for good. Three more to go. Thanks for all the help. HS
  16. hammerslammer

    hammerslammer New Member

    Messages:
    68
    Location:
    Colorado
    I got all 4 installed, working, and inspected. Looks like electric is running about the same $ for these appliances as the gas for this area, ($.07/kw), with about three people in each unit. I suspect that larger families would make a difference.

    Thanks again for all the help.
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