Mr. McIntosh, a semiretired chemistry professor in Morris, Minn., is among the growing ranks of enthusiasts who use powerful computers to "mine," in insider parlance, "bitcoins," an unregulated digital currency.

 

Mr. McIntosh keeps his specialized computer, which he said cost about $1,500 and is custom-built to find bitcoins, near the chimney flue in his basement to try to get rid of all the heat it generates.