The conversion factors you need for the exam (1 hp = 746 W, 1 kW = 3,412 BTU/h, 1 ton = 12,000 BTU/h), the direction rule, and worked problems: a 4.5 kW element is 15,354 BTU/h, a 20,000 BTU/h heater draws 24.4 A at 240 V, and heating 50 gallons by 70 F takes about 1.9 hours. Includes the BTU vs BTU per hour trap and a timed quiz.
Free voltage drop calculator that shows every step:
OhmPrep Calculations Course (308 exercises, 4 timed practice exams):
Full written guide:
Sources:
NIST Special Publication 811, Appendix B.8, Factors for Units Listed Alphabetically:
U.S. Energy Information Administration, British thermal units (Btu):
USGS Circular 1268, Conversion Factors (1 gallon = 8.34 pounds):
U.S. DOE Building America, Strategy Guideline: Proper Water Heater Selection:
OpenStax, University Physics Volume 2, 9.5 Electrical Energy and Power:
Check the code edition your state has adopted and ask your local authority having jurisdiction (AHJ). OhmPrep is an independent study tool, not affiliated with NFPA, the National Electrical Code, or any state licensing board.
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