ANSWERS: 2
  • about 30 seconds.
  • This depends on your method of heating the water. Here in America, we generally use water heater tanks to heat our water. If you look on your heater tank it will tell you the capacity in gallons and the amount of energy it uses to heat in british thermal units (BTU's) or in watts/kilowatts (W/kW). To use an equation to find out how long it will take you have to know some descriptions and conversions. 1. 1 BTU is the amount of energy it takes to increase the temperature of one pound of water one degree Fahrenheit (F). 2. 1 W of energy equals about 3.4BTU/h. **For example, lets say your heater says it uses 4000 W (or 4kW) then you would multiply 4000 X 3.4 to get 13,600 BTU's.** 3. 1 U.S. Gallon (gal) of water equals 8.3 pounds(lbs). 4. On average, water enters your home between 45 and 55 degrees F. This is used to establish change in temperature or Delta T. **For example, guessing your water coming in is 50 degrees F and your heater is set at 110 degrees F, your change in temperature (Delta T) would be 60 (110-50=60) The equation is the number of gallons in your tank times 8.3 pounds (the weight of a gallon) times the change in temperature, divided by the energy your heater uses (sometimes in watts but the equation must be in btu's). [gal X 8.3 X (delta T)/btu] So let's say your heater is brand new and it can hold 40 Gal, is rated at 30,000 BTU, and is set to 120 degrees (with 50 degree water coming in), the equation would be: 40 X 8.3 X 70 / 30,000 = .77466666e Just round that to .775 and multiply 60 X .775 to get 46.5 minutes. Thats how long it will take to heat the water in this situation. Remember to find your numbers needed on your heater and if you want to be really accurate you can try to test the temp of your water coming from your cold water tap. As time goes by, your heater becomes less efficient and will not necessarily use that max BTU rating.

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