While I’ve been active here at bitcointalk for nearly a decade, I’ve avoided getting involved in mining.  It’s been my opinion that, given my local cost of electricity, the cheaper way for me to acquire bitcoins is to buy them, rather than mine them.  However, a few variables have changed recently, and I’m thinking about dipping my toe into the mining pool.  I know that, if I’m going to do this, I’ll need to acquire some sort of ASIC, and I’ll need to figure out how to get it set up.

Here’s the situation…

I now have an electric vehicle, and as such I now have 240 volt 60 amp circuit run to my garage.
I’ve recently insulated my garage to retain some heat.
I live in the Chicagoland area where outdoor winter temperatures regularly drop to -10 Celsius.
My garage doesn’t currently have ANY heating service run to it.

My thought (hope?) is that I can set up an ASIC in my garage, and generate enough heat this winter to keep the temperature in the garage above 0 Celsius while paying for the cost of heating the garage via the BTC generated by the ASIC.  Essentially, the ASIC (hopefully) becomes a garage heater that pays for its own electricity. At the end of the winter, I'd sell the ASIC (assuming I was able to maintain at least break even on the electricity for the duration), so the total cost of heating the garage for the winter would just be the difference between the purchase price and sale price of the ASIC.

I’m trying to figure out how efficient (MHash per Joule) the ASIC needs to be to break even on the electricity used at current difficulty and bitcoin exchange rate. I’m not sure if I’ve got the maths correct, and I was hoping some experienced miners here could check my calculations and let me know if I’ve messed up somewhere.

Here are the values I’m using for my calculations:

- Local electricity cost = $0.13 / kWh
- Current BTC exchange rate: $50,000 / BTC
- Current Satoshis earned per ExaHash: 7668 sat/EHash

Using those numbers, I seem to have calculated that I’ll need an ASIC that generates at least 9,418 MHash/Joule to earn the $0.13 per kWh that I’ll need to break even.  Does that sound right?  Did I mess up the calculation somewhere?  If so, can you explain the correct calculation for me?

Once I understand the correct calculation, I'll set up a spreadsheet where I can regularly update the electric rate, exchange rate, MHash per Joule of the ASIC, and difficulty to determine if I'm still earning at least my cost. That way I can shut off (and sell?) the equipment when it is no longer breaking even, or just avoid buying the equipment at all if I'm not going to be able to break even from the start.