Wire size for 120V water heater?

Discussion in 'Electrical Forum discussion & Blog' started by Artie, Oct 3, 2010.

  1. Artie

    Artie New Member

    Messages:
    46
    Location:
    Jacksonville, Fl
    I want to run this water heater, (10 gal., 120VAC, 1650W), at a remote location. (Approximately 20ft. from the breaker box.) Would 12-2 be sufficient?
  2. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    1650 watts is about 13 amps. 12 guage wire is fine.
  3. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    If you have an ohmmeter, before you install this heater check that the element resistance is at approx. (120v^2)/1650w = 8.7 ohms.
    It can't hurt to make sure.

    Their kwh rating for a year is based on it being on 17% of the time. I guess this is some consumer average usage.
  4. Artie

    Artie New Member

    Messages:
    46
    Location:
    Jacksonville, Fl
    Thanks guys.
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,296
    Location:
    Cave Creek, Arizona
    The KW for a heater is the "actual" wattage, not a "kw per year" statistic. The "kw/yr" number creates the "annual cost of operating the heater" which is a completely different thing.
  6. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Speaking of power usage,
    since the element runs on 120v, wiring an electromechanical analog clock across the element for 24 hours or so will tell the heat loss through his R8 insulation.
    If the clock advances 5 minutes every 600 minutes with no hot water being used then his loss is 1650w(5m/600m) = 14 w = 48 BTU/hr.

    I definitely have to find a day job. . .:)
  7. Artie

    Artie New Member

    Messages:
    46
    Location:
    Jacksonville, Fl
    Thanks. 1650 is the "watts @ 120VAC". 2523 is the Kw hours per year.
  8. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,569
    Location:
    North Carolina
    A #12 on a 20 amp breaker is just what the doctor (NEC) ordered.
  9. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    Do you really think all this effort is worth it? Do you really think someone wants to go without hot water just to find out heat loss? Since heat loss should already be figured into the operating cost the energy star label should already tell whether the heater is efficient compared to other heaters.
  10. nukeman

    nukeman Nuclear Engineer

    Messages:
    711
    Location:
    VA
    It is only something us engineer types would be interested in. :)

    Anyway, if the OP wanted to know the heat loss, there is no need to do the test for 24hr. You could simply do it say overnight (or while at work). Just need to ratio the time the clock runs to the total time that has past and multiply by the heater power. Testing over a longer time would give a better average heat loss estimate, but the loss shouldn't change much unless you have the WH in an unconditioned space such as an attic or garage. In this case, the heat loss can be quite different than what the unit is spec'd at depending on climate and time of day/year.

    The test doesn't get you much except for the knowledge of how much heat is being lost. It is good info to have as a baseline to see what impact insulating the piping, replacing with a new unit, etc. has. You could also use this to show others (and yourself) that the standby loss in a tank-type WH (especially electric ones) is quite small and that a tankless type is not going to save a ton of money by not "heating water around the clock".
  11. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Mr. Port, as a courtesy to you I must tell you that you are on my ignore list.

    If this were the real world you would, right now, be a defendant in an action for harassment and defamation, at the very least.
  12. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    If he is on your ignore list, be sure not to respond when he defames you again.

    But I am more on Mr. Ports side. No one has the time for that except a high school energy class.

    Tankless water heaters are pretty much a joke when compared to an electric rig. You can bury an electric water heater in all your old winter jackets and get the standby losses to near zero.

    And I think the Indian-Indonesian anti-defamation league will soon be contacting you about that kid in a bowl about to be eaten by a snake.
  13. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    27,296
    Location:
    Cave Creek, Arizona
    A 24 hour reading would only tell you the TOTAL time the heater ran, including replenishing the hot water used, unless the system were not used during that time period. If the heater is in an "unconditioned location" such as a garage, the heat loss will fluctuate according to the ambient temperature, which could change hourly, and would definitely change during the various seasons.
  14. Artie

    Artie New Member

    Messages:
    46
    Location:
    Jacksonville, Fl
    I'm interested in all opinions here. My situation is that this old house's water heater is too far from the kitchen sink. I hate the fact that I must wait 5 minutes to get hot water from the kitchen sink. I was thinking of doing a small dedicated heater just for the sink. On the other hand, I don't want to spend $400/yr to do that. But I might, for the "luxury" of psuedo-instant hot water. All opinions and ideas welcome. :confused:
  15. Jim Port

    Jim Port Electrical Contractor

    Messages:
    156
    Location:
    Maryland
    You could see about adding a recirculator pump on the hot water line. This way you should not need to wait so long for hot water.
  16. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Last edited: Oct 6, 2010
  17. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Its a pity that a 10 gallon water heater costs more than a 50 gallon job.

    You can find a 20 gallon mobile home one for 250$ or look at motor home water heaters, and get a small 120 volt element, maybe 1200 or 1500 watts, and you could plug it in under the sink without more wiring. That would likely be cheaper than a recirc system, and you can super insulate the unit too.

    If you use a lot of water at that sink, your incoming cold could be the HOT in from the water heater. That should fill in the "lag" time
  18. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    You only have to make up 1 gallon of cold water per 100' of 1/2" ID pipe. It's ~800 BTU for a 90F rise, so using 1200 W it'd take ~11 minutes to recover.

    You probably have the whole morning to recover. A 120w heater will take 1.8 hours to recover.

    Decide on what tradeoffs you can make and then hope somebody makes a heater that does this.

    8.3 pounds/gal
    90 F rise
    747 =BTU

    according to
    http://www.onlineconversion.com/
    this many BTU per hour equals
    219 watts

    with 1200 w
    this takes
    0.1825 hour
    10.95 =minutes
    Last edited: Oct 7, 2010
  19. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Right, so a 1200w or less 5 or 10 gallon WH under his sink, with the hot from normal heater as infeed would solve his issue pretty cheaply with less issues than recirc.

    Would also keep his undersink warm and dry, an advantage toward cabinet survival.
  20. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Yes, I hope we find out how it finally worked out. The OP certainly has all the facts by now.

    Mr. Valve, you are definitely not a run-of-the-mill electrician.

    Good. You can make up for the [name deleted] types in this world.
    Last edited: Oct 10, 2010
Similar Threads: Wire size
Forum Title Date
Electrical Forum discussion & Blog Breaker and wire size for pool heat pump - MCA, wire and breaker size. Feb 28, 2014
Electrical Forum discussion & Blog Wire size, 3ph Delta, 120/240 Jul 10, 2012
Electrical Forum discussion & Blog Wire size Feb 20, 2012
Electrical Forum discussion & Blog Neutral wire size smaller than hots for 100 amp subpanel? Feb 10, 2012
Electrical Forum discussion & Blog Sizing Kitchen Range Breaker Size & Wire Gauge Apr 12, 2011

Share This Page