My household uses surprisingly little electricity during the summer, probably because we don’t run the AC much. Air conditioning is expensive, especially with an elderly outdoor furnace/AC unit that was manufactuered before Facebook was a thing. Without the AC’s 3.5kW draw, our electric bill stays nice and low most months–except when it doesn’t, for (seemingly) neither rhyme nor reason.

While investigating the months of higher electricity usage, I noticed that the house draws about 420W on average–at night. I was surprised that our baseline usage was that high, so I bought myself a Kill-A-Watt meter to see what was going on. The device is dirt simple. Suppose you have a thing, and you’d like to measure its electricity draw. You plug the meter into a wall socket. You plug the thing into the meter. You push buttons to switch between amperage, wattage, overall power consumption (in kilowatt-hours), and time since the meter was plugged into the wall. Bam. Profit.

With the last two items, you can estimate the average electricity draw over a long period of time. Dividing the total consumption (in kilowatt-hours) by the time the equipment has been running (in hours) nets you the average electrical draw over that time period (in kilowatts). This is useful for devices with intermittent load, like refrigerators.After some unscientific experiments, I got some numbers on instantaneous power draw from my old hardware:

• LCD monitors use about 30W apiece when on.
• Wireless routers use 3-5W of electricity when idle.
• Wired router (a Celeron desktop) uses 45W idle and 65W when under full CPU load.
• T43 laptop uses 5W in standby (not charging), 25W idle, and 50W under load.
• Desktops use about 5W when off/standby.
• i5 + nVidia GeForce 650TI box uses 45W idle and 90W playing Unvanquished.
• i7 + AMD 6950HD box uses 99W idle (!), 240-260W playing Deus Ex: Human Revolutions, and 300W (!!) playing Bioshock: Infinite.
• Core 2 Quad server with four hard drives uses 150W of electricity.
• Acer h340 NAS uses 56W under full load with the case fan at 100% and all four hard drives spinning.

Immediately I spotted some things that were using far more electricity than I had assumed. The Core 2 Quad box is one. In retrospect, the waves of heat pouring out the back of the case should’ve been a hint. I took its 4 hard drives and put them in the NAS. It uses a third the current, and while its CPU is sloooooow, it does do what I need it to do, and I can accept the loss in performance. The wired router is another device that could be replaced to save. In addition, LCD monitors use more electricity than I realized; I’m making a concentrated effort to turn them off when I’m not around, or to configure their power saving modes more aggressively.

I’m going to go back and measure every device I have using a more rigerous method, noting down phantom power (draw when off), standby power (when applicable), idle draw, and loaded draw (under various CPU, hard drive, and GPU workloads). Eventually I’ll get a table of hardware set up here with various figures.