Water heater kWh use?

Discussion in 'Water Heater Forum, Tanks' started by NancyHawaii, Jan 16, 2014.

  1. NancyHawaii

    NancyHawaii New Member

    Messages:
    5
    Location:
    Washington
    My nephew moved into his apartment last month for 5 days then was gone for the next month. Just received his first bill, from 12/5 to 1/10 (he was only there from 12/5 to 12/10), the kWh used was 289.

    When he was gone, we couldn't find which breaker for the water heater so couldn't turn it off. Other than water heater and refrigerator, everything else was shut down.

    The water heater is a small 40 gallon under the kitchen cabinet.

    I'm assuming, although the water heater was on, it still used less electricity because it was just keeping the water hot as compared to when he's home and running the hot water?

    I thought the usage would be alot less than 289 kWh. I did some research and for a small apartment refrigerator, it would consume about 50 kWh per month...so that would mean the water heater consumed almost 240 kWh/month when the apartment was empty??

    Thanks...any clarification would be greatly appreciated.
  2. tvl

    tvl New Member

    Messages:
    138
    Location:
    South Carolina
    Water heaters are energy hungry appliances. Although your nephew was gone for practically the entire month, the unit continued to keep the water at the desired temperature. And, if the comfort heating was turned down during this time, that could have played a small roll in making the water heater run a little more often. Anyway, following is an example of water heater usage I pulled from the net:

    Water heater.jpg
    That is 375 - 425 KWH per month (these units normally have 4,500 watt heating elements - that is the same as 4,500 100 watt lamps burning)

    The refrigerator and water heater could have easily used this much energy ...................... and I'm sure there were other small appliances that were possibly left on: alarm clocks, night light, etc.
    Last edited: Jan 16, 2014
  3. Dana

    Dana In the trades

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    2,783
    Location:
    01609
    Electric hot water heater standby loss is pretty low, but it could account for almost half of that 289kwh.

    A refrigerator uses quite a bit more than the efficiency ratings would indicate if it's in a non-air conditioned space in Hawaii (assuming that's where you are) that is allowed to stagnate at 85F or higher.

    Insulating all of the near-tank plumbing to at least R4 (5/8"-3/4" closed cell foam pipe insulation) including the cold-feed to the tank and the temperature/pressure overflow drain will cut the standby loss of an electric hot water heater by about a third. Turning the thermostat on the tank all the way down while you're away also works. Don't take half-measures though, you want the tank temp to either be above 120F or below 85F to limit the risk of pathogen colonies getting established.
  4. Reach4

    Reach4 Active Member

    Messages:
    1,883
    Location:
    IL
    He shut off the heat?
    Consider a Kill-A-Watt for testing the fridge and more. http://en.wikipedia.org/wiki/Kill_A_Watt It won't work for the water heater.

    He could have used considerable power during his 5 days.

    Any chance of an estimated bill, tho in that case, the bill would have been higher probably. Maybe a partial-month estimated bill?
    Last edited: Jan 16, 2014
  5. NancyHawaii

    NancyHawaii New Member

    Messages:
    5
    Location:
    Washington
    Actually, we unplugged everything else during the time he wasn't at the apartment (i.e. microwave, lamps, etc..) and turned off the heat. Only thing that was on was the water heater and refrigerator.

    I'm just curious because he was only here for 5 days and the bill was for 36 days billing... is his next month's bill going to be 7x the cost of 1st month's bill? since he was only here 1/7 of the time in December.
  6. NancyHawaii

    NancyHawaii New Member

    Messages:
    5
    Location:
    Washington
    He's actually in Seattle.

    How much energy does the water heater consume when it was ON but not being used as to compared when its being used and heating up?
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    You may be able to look up the energy label for that WH model on the internet. Depends on how warm or cold it was in the apartment, how high the thermostat was set on it (maybe more correctly called aquastat), and whether the pipes are insulated. Does the place have a recirculation system? Are there any valves dripping (shower, sink, etc.)?

    Once you get the water hot, how often it then needs to come back on will depend on use, the quality of the insulation and if the pipes are insulated, otherwise, they act like radiators.
  8. Reach4

    Reach4 Active Member

    Messages:
    1,883
    Location:
    IL
    If he used 7x as much electricity, the bill would not cost 7x as much. Some charges are fixed costs. Plus the first KWH cost more in most places. And he is not going to use 7x as much electricity.

    The temperature setting on the WH would have made a difference in consumption too.
  9. JerryR

    JerryR Member

    Messages:
    231
    Location:
    Florida
    If he moved into an apartment where electricity was off and he turned it on he paid to bring the water temp up from cold to 120 deg or so.

    I have a home that I was only at 6 days between Thanksgiving and Christmas. I used 325 kWh during that 32 day billing period. When I was gone I turn off water main and throw the water heater breaker. I have some lights on timers, refrigerator running, fax machine, answering machine, Internet modem, wifi router and 4 cameras running 24/7. The 4 ton air conditioner logged 27 hours of compressor run time during that period.

    The bill for that 33 day period was $41.21 for 325 kWh.

    My lowest bill where I was gone all month was $28.84 for 200 kWh with water heater turned off an no air conditioning or heat usage.

    Looking at my bill, there is a fixed base charge of $7.24/month. Usage charges are on top of that $7.24/month charge.

    JR
    Last edited: Jan 16, 2014
  10. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    In a wintertime Seattle climate with the heat off, the standby loss of the water heater rises, and the energy use by the refrigerator falls.

    The EF test numbers for older electric tank hot water heaters run in the 0.90-0.92 range. What that means is that for a 63 gallon/day hot water user, 90-92% of the power use was in heating up the water, 8-10% was lost, heating up the room. (Newer efficiency standards going into effect next year will reduce that to a 3% standby loss under EF test conditions.)

    The standby loss of one of those so-so not super-efficient electric water heater in a 65F environment is about 75 watts, or 0.075 kilowatts. Those losses will be higher if the water is maintained at a higher storage temp or the tank is in a colder room, but unless the apartment temp dropped below 40F (in danger of freeze-up) it won't be anything like 2x that figure. Over 36 days that 24 x 36=865 hours, so the kwh use would come to about 865 x 0.075= 65 kwh. A really great electric hot water heater with well- insulated near-tank plumbing would have standby losses about half that. If the apartment was REALLY cold you're looking at less than 100kwh in standby loss on the water heater for that period.

    If the heat-traps on the inlet/outlet plumbing aren't working the standby losses can be more, but not 2x.

    I suspect the bulk of the power use during his absence was the refrigerator, which can be pretty high if the weatherstripping is leaking or the refrigerant charge has bled down a bit. There is also the off chance that the calibration of the electric meter is way off (it happens), or a circuit of one of the other apartments is wired to his meter (which also happens.)
  11. NancyHawaii

    NancyHawaii New Member

    Messages:
    5
    Location:
    Washington
    Unfortunately, the water heater is under the kitchen cabinet and i rather not mess with it :)
  12. NancyHawaii

    NancyHawaii New Member

    Messages:
    5
    Location:
    Washington
    His bill was only $19.66 of which $5.69 was 'based service charge'...so total for the the 36 days was only $14. I was just thinking $14 accounted for 1/7 of the days, hopefully his monthly bill won't be $14x7=$98 for his small apartment :)

    Seattle's kWh is $.0475 or $.0506 depending on the time of day i think...in Hawaii, we are paying $.36 kWh no matter what time of day :(
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    Most utilities divide their bill up into three parts: customer charge (fixed for the type of service), electricity production charge, and electrical transmission charge (covers costs of wiring, poles, taxes, transformers, etc.).
  14. Dana

    Dana In the trades

    Messages:
    2,783
    Location:
    01609
    Reach4: "Plus the first KWH cost more in most places."

    Very few utilities are discounting high-use kwh for residential rate structures- it's often the other way around- the first 500kwh or so cost LESS, with a surcharge tacked on to subsequent power use to promote conservation. The standard residential rates for PSE is about 9 cents/kwh but only for the first 600 kwh, after which it steps UP to 11 cents.

    But "all-electric" customers in PSE territory (and elsewhere) have special rate structure for those heating with electricity- not sure if that applies to this situation, but if the "...$.0475 or $.0506 depending on the time of day..." is correct, it sounds like one of those, and not the standard fixed residential rate structure.
  15. WyrTwister

    WyrTwister New Member

    Messages:
    6
    Location:
    Texas
    I would consider putting a water heater blanket on it . And figure out what circuit breaker turns it off ? It should be something like a 2 pole 30 amp .

    God bless
    Wyr
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