Energy detective

Detective silhouetteEver since I learned that a 3 kWh a day lifestyle is achievable, I’ve been very curious as to our current usage. Since everything we have is electric (and much of the 3 kWh number is based on offloading things like heating to natural gas), I thought I’d have to wait until we actually moved.

Then I got this month’s electrical bill and realized that it’s about as good as it’ll get anywhere. We obviously didn’t use any heat this month but we also didn’t use much, if any, cooling. Given that, the only significant difference between here and the house is that here we have an electric stove. However, I think we use the stove for about half an hour a day (on average), which only adds up to 1 kWh a day, so that’s pretty easy to adjust for.

This month, we used 200 kWh over 28 days. That’s a little over 7 kWh (modified to 6 if we take off the electricity for the stove), which is about twice my eventual goal. That still seemed like a lot, so I decided to track down where all of that electricity is going.

Least surprising to me is that our refrigerator uses up to 3 kWh a day (50% of our presumptive housing number!). The refrigerator at the house only uses 2 kWh a day, which will help some as well. A new EnergyStar refrigerator can use as little as 1 kWh a day, so there’s room for improvement there as well.

So now we’re down to 3 kWh a day that are unaccounted for. The next things I thought of were basic appliances that we run intermittently, like the dishwasher, washer, and dryer. We haven’t used our dryer this month (hooray clotheslines!), but we wash dishes and clothes about once a week. That puts the dishwasher at about 0.3 kWh a day and the washing machine at 0.5 kWh a day. More efficient appliances would help some, but since we run them so infrequently, they’re not big culprits.

That puts us at 2.2 kWh a day that disappear into the unknown. I thought it might primarily be lighting, but that would be enough to run our lightbulbs for 110 hours a day, which seems unreasonable. It’s hard to estimate light usage, but I think we use about 24 light-hours a day (since mostly lights are off during the day and while we’re asleep and Maggie and I tend to stay in the same room and use one light in the evening). That’s only 0.1 kWh a day (thanks, CFLs!).

Not much of a change, but we’re down to 2.1 kWh. There are some other appliances that we use occasionally, like a microwave and clock radio, but they probably use less than a tenth of a kWh each, so that still only brings us down to 1.9 kWh. If we didn’t have most of our appliances on power strips, I’m sure that phantom power would increase this number considerably.

Oh, computers, of course. Maggie and I both have laptops. She uses hers about half an hour a day (at least, at home) and I leave mine on about 10.5 hours a day. With an average useage of 30 watts (based on 45 watts when in use and 10 watts hibernating), that comes out to a third of a kWh a day.

Well, 1.6 kWh is better but is still a lot of “black” energy. In fact, it’s 26% of our presumptive electrical use! If it takes you less than a day to figure out where that energy is going, you’ve got me beat. I’ll give you a minute to think about it.


The culprit appears to be our hot water heater. It’s stuck in a closet and we never think about it except when it’s not working and yet it’s using half as much energy as a refrigerator! It would be even more except that Maggie and I use it infrequently (especially in the summer). The EnergyStar sticker on the side says that it’ll use 4773 kWh a year, which is over 13 kWh a day! Obviously, the sticker is way overestimating (and we’re using less hot water than the typical family), but that’s still a lot. Even though it’s “only” using 1.6 kWh or so now, when the weather is cooler and it has to work harder and more often, I bet it uses at least as much energy as our refrigerator (which will be working less hard in the winter, so this is about as bad as it should get).

A tankless water heater is looking better and better! A conservative estimate would put the tankless water heater at about half the electricity as an electric tank water heater. That still puts us well over 3 kWh a day, but add in a better refrigerator and we’re starting to get somewhere! this!

4 Responses so far »

  1. 1

    Kim said,

    July 21, 2008 @ 9:59 pm

    Hmm. Interesting.

    The other day we received our first electrical bill at a new apartment. I was kind of aghast, thinking that it seemed high.

    However, having just moved from an apartment we shared with two other roommates, I didn’t have immediate access to our previous bills, and wasn’t sure what kind of usage, in terms of kwh usage, we were coming from. I knew that it seemed reasonable for four of us. And I felt that the new bill, for the new apartment seemed high for just two of us.

    However, after reading this post, I checked the bill again, and am now shocked as it would seem that our daily average was right at 3 kwh. Now I’m feeling a bit better- A LOT better in fact. But given that we didn’t quite live here a full billing month, and haven’t spent a lot of time here since we moved in, I’ll be looking to track this more closely…and use the 3kwh a day as my continuing goal.

  2. 2

    Water heating is a tankless job | said,

    August 25, 2008 @ 7:21 pm

    […] abstract thinking about a tankless water heater became more concrete recently when we realized that our (25-year old) water heater was broken. Not […]

  3. 3

    Slaughtering an Energy Hog | said,

    September 5, 2008 @ 8:44 pm

    […] high as 200 Watts.  With 24-hour usage, that adds up to 6 kWh per day, almost as much as we used in our old apartment in July.  Craziness.  Of course, it will be awhile before we see any significant savings in our energy […]

  4. 4

    Laptop Power | said,

    March 19, 2009 @ 12:12 am

    […] two weeks). That averages out to about 1.75 kWh per day. That certainly makes it hard to hit my 3 kWh a day target but it’s slightly better than my 2 kWh per day […]

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