Home / Other Calculators / BTU Calculator The BTU Calculator can estimate the amount of BTUs you will need to heat or cool your home, based on the size and the temperature you want for your home.Please note that this calculator can only gauge a rough estimate. You should also consider factors like efficiency decrease of the heater or air conditioner with time, the shape/type of your home or room, insulation conditions, and other factors. 1 watt is approximately 3.41214 BTU/h. good (very few leakages or windows) poor (many leakages or windows) Temperature to Increase or Decrease Depending on your local winter/summer temperature,e.g. 75F for Boston winter, 35F for Atlanta winter. Free Estimation of Your Heating or Cooling Project >>Reference The British Thermal Unit, or BTU, is an energy unit. It is approximately the energy needed to heat one pound of water for 1 Fahrenheit. 1 BTU = 1,055 joules. 1BTU/hour = 0.293 watt. One very well-insulated 1,000-square-foot home in Boston needs around 24,000 BTUs to heat in winter.