Re: It only costs 100$ in electricity to mine a bitcoin???
Those god-damned oil furnaces are STILL legal in NYC?! 
You may's well just get a barbecue oven, go collect as much plastic trash as you can find, and light it on fire in your house. You could pay off the mining hardware (mining revenues excluded) within a couple years if you switched from oil to electric mining. Mind successfully fucked, though.
It makes the most sense to buy moderate amounts of miners at the retail level if you live in a cold part of the world, as you can position the miners near windows and other cold parts of your house to serve as a replacement to your heating. This allows you to essentially have free electricity during the cold parts of the year. You may's well just get a barbecue oven, go collect as much plastic trash as you can find, and light it on fire in your house. You could pay off the mining hardware (mining revenues excluded) within a couple years if you switched from oil to electric mining. Mind successfully fucked, though.If there weren't heat exchange systems which provide not only an heating efficiency in excess of 200% but also offer cooling and dehumidifying which also cost less then a mining rig that argument would actually make a just a little sense. And if it's so cold that these systems no longer work you'd be investing a lot more in insulation and probably have a natual gas line.
But there is also noise and uncertain viability of maintaining any profitability from mining all, not to mention the unreliability of the devices itself...