I have a Rockminer R3 / 500GH that I recently retired.
Was heating a friend house for last 3 winters.
Great runner, unbreakable. It run on Pi via USB hub to 4x boards.
Also have P/S I can spare to run it.
It's probably a bit bigger than what I'm looking for. I don't really need to heat my garage

You don't have anything smaller and less power intensive?