Um, when asking such basic questions you should learn how to use google or other search engines...
Search for "watts to BTU" and you will get your answer.
If running 2 or more just multiply by how many miners
i googled but the most of calculators are for thermo or airconditioner and a server-farm with fans is not the same like hydro mining. i think u cant calculate it with 3.412 on hot water
Yes you can. Heat & power equivalence is the same no matter if it is carried by air, water, oil, metal, etc. The equations are the same. The only thing that changes for fluids (air is considered a fluid) is the mass flow rate needed to carry x amount of heat from one place to another. For metals or other solid materials it is thermal conductivity that controls rate of thermal transfer.