Here is my working room heater
I have a wooden custom build case under my desk with big ATX chassis in it, and one undeclocked Avalon4 connected to my Linux workstation which is always powered on anyway
Avalon4 is connected directly to my PC's power supply
My PC is an good old Intel quad-core, custom water cooled with water cooled GPU (an old AMD, doesn't even support OpenCL, so I can't mine with it
But my undeclocked Avalon4 at only 30% fan speed is almost totally silent and at 45C it makes a great foot heater for cold days
That makes a nice heater that actually makes Bitcoins ... the miner itself draws about 380W which makes lesst hen 0.55 W/GH at wall ... considering the heating effect the electricity is basically free.