I got an old bucket and lined it with tin foil to reflect the heat.
I have a bucket lined with tin foil facing the back of a computer that is currently producing Vanity Bitcoin Addresses to help with fund raising of various projects. Inside the buck goes a bottle of water with a thermometer on it so that I can measure the temperature.
I am monitoring the power consumption as I go.
I am monitoring the power used by a computer. Next let's see what useful work the computer is performing to produce the heat.
VanityGen UI comiled from Xcode on OSX
Temperature gets up to about 37 degrees celsius. With an amient room temperature of about 25 degrees.
I then use the water in the kettle to make cups of tea, saving a small amount of electricity because I can captured some of the excess heat from the computer. I also use it to dry out socks and things.