Measuring my Electricity Consumption?

January 9, 2009 11:44 PM

How to accurately (and cheaply) measure my electricity consumption?

I rent a room from a lady (fixed cost), and she informs me that her electrical bill has skyrocketed since I moved in. She says the bill is $76 more than the same period last year. Not sure what she was paying for a kWh last year, though we can determine that.

I would like to pay her for the extra electricity used. Utilities are included, but I'm getting a great rate for this place, and she's a family friend, and I'm looking to do the right thing.

I know a lot of the extra money on the bill comes from my computer, but a $76 increase seems excessive for what I use.

$76 would be about $2.55/day, which is about 25.5 kWh/day (assuming $0.10/kWh, can find out what she pays), which is 1063 Wh, every hour of the day.

My Equipment:
Mac Pro Quad 2.66
This is on 24/7, and is idle probably 18-20 hours a day.
171W idle, 250W max.
4 Hard drives, two of which are WD Green drives. Set to go to sleep when possible.

Dual Dell 2405fpw flat panels
Off when Mac Pro is idle, both on when Mac is being used.
120W when on, 2W idle, for both.

32" LCD TV, on an average of 30 minutes a night.
Apple TV and Stereo receiver, always plugged in, only on when the TV is being used.
Misc lights and alarm clock, nothing major.
Unless my math is wrong, at $0.10/kWh, these numbers should add up to about 1063, and they aren't coming close to that, even if everything was on 24/7 and the Mac was running at full load.

So, to my real question. How can I accurately and cheaply measure my electricity consumption? I would like to pay for what I use, but it seems like $76 is too much for what I use. There is also another tenant on this house, and everything is on the same meter, but I doubt he is using anything major.

What can I buy, preferably local, that will allow me to measure my consumption? Thanks much.

posted by santaliqueur to computers & internet (21 comments total)

Maybe a few of these to measure how much your major appliances are actually using?
posted by Chan at 11:50 PM on January 9 [1 favorite has favorites]

Some libraries have the Kill-A-Watt available to borrow, worth checking in to save a few bucks.
posted by Chrishartley at 11:58 PM on January 9

Is the water heater gas or electric? It takes a lot of energy to heat water and one assumes you're also bathing regularly.

To give you an idea, somewhere I saw a page where they were using a swimming pool as the reservoir for their water cooled server bank. Think like 10 or so of your setup and you'll probably have a pretty good idea of how much computer they had running. Not only was this not effective at making the swimming pool warmer, the water in and water out temperatures were within a half degree of one another.
posted by Kid Charlemagne at 12:11 AM on January 10

25.5 kWh/day is a bit over one kW, which might be an easier number to compare with your electronics.

Maybe you take longer hot showers (25.5 kWh = 86 kBtu = 40 minutes of showering?) or keep the thermostat set higher than the last person. Or you leave your two 500W halogen torchieres on all the time?
posted by hattifattener at 12:22 AM on January 10

The best way of doing this is to look at her energy bills. If she won't let you do that, any assertion that her power bill is more than it used to be will be completely unverifiable. Most utility bills not only contain last month's consumption, but previous months as well. You could spend a lot of money on this trying to figure out exactly how much your appliances use, or you could just look at her bills and do the math.
posted by valkyryn at 3:24 AM on January 10

Just curious, why do you leave the Mac Pro on 24/7? You could have it go to sleep when inactive for a certain amount of time. It's using more than 171/250 if you've got more than two sticks of RAM in there. In fact, the FB-DIMM modules are known to use about 14W each, as they each have a little hungry microcontroller in them.
posted by floam at 3:24 AM on January 10 [2 favorites has favorites]

Do you have electric heat? Maybe you keep the room temperature warmer than the previous tenant.
posted by weapons-grade pandemonium at 5:28 AM on January 10

I know a lot of the extra money on the bill comes from my computer, but a $76 increase seems excessive for what I use.

$76 would be about $2.55/day, which is about 25.5 kWh/day (assuming $0.10/kWh, can find out what she pays), which is 1063 Wh, every hour of the day.

I live in a terrace house in England with 4 other people. We all have computers, but not computers as power-hungry as yours (i.e. some people only have laptops), and people turn their computers off when out of the house.

In the past 2 years we have used, on average, 8.8kWh/day of electricity (computers, appliances, cooking); and 16.6kWh/day of natural gas (hot water inc. shower, and heating); for a total of 25.4kWh/day for 4 people. In other words, 6.3kWh per person per day.

So I would say if you personally are using 25.5 kWh/day your usage is comparatively high.

Here are some other possibilities: 1. Your power company raised its rates; 2. Your conversion from cost to kWh is inaccurate; 3. Estimated meter readings getting out of sync with your true meter readings, either last year or this year; 4. Meter misread (easy if it's one like this one; 5. Bills actually for different periods (I've received bills for a single day in the past).

So, yes, I second the suggestion of a Kill-A-Watt; and I also suggest you look at the power bills in more detail so you know the actual number of kWh you're talking about.
posted by Mike1024 at 5:36 AM on January 10

So I would say if you personally are using 25.5 kWh/day your usage is comparatively high.

Don't forget that in the US (land of cheap energy), stove-tops and water heaters are commonly electric; electric furnaces are surprisingly common in houses built in the 1960s or so, too, believe it or not; and a lot of houses are heated by electric baseboards. Even so, from a quick google search, it looks like a typical US household in a single-family (detached) house uses something on the order of 10,000kwh/year (lots of numbers here; regional differences are huge, though, so don't take "typical" as really being all that typical). Assuming a household of three people, that's only about 10kwh/person/day, which suggests that your 25kwh/day is on the high side.

Back to the original question, here is a page explaining how to directly read your consumption off of the power meter. You'll want to pick a time of day when the other tenant isn't home, and make sure that no big appliances are kicking on and off. Turn everything in your room off, measure, then turn everything on and measure again -- that'll give you your worst-case, maximum-consumption figure for your room. But on top of that, you need to assess how much household electricity you are using (water heating, oven, HVAC, lights, etc) and pay your fair share of that, too.

In the end, since you say you are getting a good deal on rent and the landlord is a family friend, you will probably want to pay an amount that leaves everyone happy, rather than some scrupulously calculated amount that reflects your actual usage. So sure, go through all the calculations, but at the end of the day those calculations don't have a lot of bearing on the amount you should pay in this situation.
posted by Forktine at 6:28 AM on January 10

Agreed that you need to start with the actual figures/bills.

We have something like the Kill-A-Watt, a bit nicer. It's pretty cool and it is very useful in assessing consumption. (We got it at a heavy discount through our electricity company, which sent out a flyer with our bill advertising the deal. It might be worth an inquiry to see if yours offers anything similar; if so, maybe you could work out something with them and/or your landlady to take advantage of it.) We are two adults and one toddler. The major power hogs in our house are: the electric dryer (worst of all!), dishwasher, stove/oven (when on, of course), microwave, and anything that uses hot water (because then the hot water heater needs to heat up more water). Our heat's a mishmash, but the major appliances are gas; however, we use an oil-filled space heater in my son's bedroom and it's not as much of an energy suck as I might think. I can't compare computer use since we just run a low-key laptop, but I wonder if, as another commenter said, it is drawing more than you think.

I'd have to go do some math/look at our bills and the monitor to see the kWh we are drawing, but our "resting" rate on the monitor is 5 cents per hour. But if we're running the dryer or dishwasher, it'll go up 60 or 80 cents; if we have a lot going on, I've seen it bump up to $1.40 an hour or so. Since we got the monitor a month or two ago, the major change I've made is to use drying racks instead of the electric dryer more often.

From your question, it sounds as if your landlady, last year, had no renter, and this year she has you? Is that correct? The bill increase still seems high, but more believable than if she is comparing your usage to that of another renter.

I wonder if it's at all possible that she got some new appliance (fridge, washer/dryer, etc.) that draws more than she realizes? Or, with the other tenant, who knows, maybe he has a souped-up computer too?
posted by Herkimer at 6:45 AM on January 10

Well, if you want to get crazy about it, as I did in a similar situation, you can go around the house and turn off everything except your stuff.

Then go outside where the meter is and watch how much electricity it measures over a given amount of time, like 10 minutes, then multiply out to hours and calculate kWh usage. Analog meters are easier to do this with since you can watch the wheels go around. The digital ones may require you to wait more than 10 minutes to get a value.
posted by odinsdream at 6:48 AM on January 10

I should say, no renter in your space? I assume the other guy was there last year, or she wouldn't believe it was you that caused the rates to skyrocket.
posted by Herkimer at 6:49 AM on January 10

Is the heating in the house electric? I have noticed that my electricity bill is going to be almost twice as much this month as it was last year, for no other reason than the fact that it's much, much colder this winter. And I saw on the news that electricity usage is at an all-time high where I live. So it might be a factor out of your control.

Unless there's a good reason not to, I'd recommend setting your mac auto-suspend after 20 minutes of inactivity. An idle computer is a major waste of electricity.

Also, I once had a tivo that I discovered was using about $12/month in electricity, even when "asleep", so I'd recommend buying a kill-a-watt and testing everything that's connected to your TV.
posted by helios at 7:44 AM on January 10

Find the electric meter and start keeping track of the number at the start of a few days period. Do thing normally and then after that period record the number again. Now turn off everything and leave for a few days while recording the starting number. Remember that things such as VCRs, alarm clocks, monitors, tvs, microwaves all are power thieves so be sure to unplug all of them. Record the number when you get back and you should have a pretty good idea of how much electricity you use per day.

If heating, water heater, stove are all gas then you may have to look at that use as well. Sometimes gas and electric are provided by the same utility so she may be including those costs in her analysis. You can either get the electric rate per KWh from her bill or the power company. Then do the math to pro-rate your few days analysis with the monthly figure to check her figures.
posted by JJ86 at 8:05 AM on January 10

Be cautious about using a Kill-A-Watt. I have one and it does read higher than my actual usage.
posted by Raybun at 8:14 AM on January 10

Your landlady is talking dollars per month and you're talking kilowatt-hours per month. Between the two is the rate in dollars per kilowatt-hour. This rate is not a constant. You need to look at the electric bills to see how the rate has changed in the past year. Since the price of oil has varied dramatically over this period, I wouldn't be surprised if the rate has changed quite a bit. (Be sure to scritinize the bill for items like a surcharge for the electric utility's cost of oil or gas that it is passing through to customers.)
posted by exphysicist345 at 9:56 AM on January 10

We are talking in those figures because they are the only ones each of us know. I'm not sure when the other renter moved in. I do most (if not all) of my bathing at my girlfriend's house, it just works out that I'm there often, and I just shower there, so my only power draw comes from the computer.

I ordered a Kill-a-Watt from Amazon, to get an idea of what I'm using. Thanks all!
posted by santaliqueur at 11:16 AM on January 10

Does the other renter use electric heat, or have an electric space heater? Maybe he likes it at 80 degrees and he's using a space heater to reach that temperature. Most space heaters use about 1.5Kw when actively heating.
posted by reeddavid at 5:12 PM on January 10

I don't know where you are, but in California we are charged more per kWh above a certain number of kWh per month. For example, my bill for this month looks like:

Electric Charges $159.57
Baseline Quantity 664.10000 Kwh
Baseline Usage 664.10000 Kwh @ $0.11550
101-130% of Baseline 199.23000 Kwh @ $0.13131
131-200% of Baseline 229.31516 Kwh @ $0.24725

As you can see, going over baseline usage can cost you quite a bit per kWh. If you have multiple people living in your house it can be easy to do this by accident, and then small increases in consumption translate into big differences in your bill. Maybe that's what happened?
posted by thalakan at 11:17 AM on January 11

I took a closer look at our meter--I didn't realize it has a simple way to display kWh. Our "baseline" rate of 5-6 cents an hour corresponds to 0.5 kW/hr, for example.

Please update when you figure out what's going on! I'm curious.
posted by Herkimer at 1:06 PM on January 11

I will update this thread as I get more information.

As it turns out, the other tenant moved in this summer, so the "$76 more than this time last year" couldn't possibly be attributed to just me. I plan to go over the bills anyway, even though I'll end up paying more than my share, since she's a family friend and I'm getting a good deal. Just don't want her to think that I'm the only reason for this increase.
posted by santaliqueur at 10:43 PM on January 11