I have a number of homemade computers which are fairly low end machines. I wondered about how much power they actually consume, so I recently purchased a meter which I can hook them up to. One of them is an Intel E5200 with 2 Gb of ram and 2 hard drives, and no video card. It's power consumption by meter was between 55 and 60 watts. Another one, an Intel E6700 with 4Gb of ram, and one hard drive, and also no video card uses about 75 watts. When I test the meter with a 75 watt light bulb, it shows about 75 watts so I assume the meter is giving me good numbers. I was surprised at how little power they drew, but nonetheless, 75 watts is a lot of heat, especially if you release it all inside a box. None of my computers have cases so temperature is never a problem. There are a couple other nice things about caseless computers; they collect practically no dust, working on them is a trivial problem, and they are very quiet. Part of my interest in doing this was to estimate how long my UPS would last. It's a SmartUPS 1000 hooked up to a couple of car batteries. My entire system load is about 500 watts, so I think the two batteries should be good for 1 to 2 hours.