Measure the length, width and height (floor to ceiling) of the main room you use every day.
Refer to the BTU calculator at the Herman-Nelson website and open a new browser window with this link.
Select Fahrenheit or Celsius on the calculator. Enter your target inside temperature and the average low temperature for a specific winter month.
Enter the length, width and height of the room you measured. Press “Calculate” to determine the needed BTUs for heating your home.
Review the BTU output of heaters and their efficiency. Multiply the BTU output by the efficiency rating; for example, 10,000 BTUs with a 70 percent efficiency rating equals 7,000 net BTU output.
Compare the figure from Step 4 and Step 5 to ensure your selected heater is sufficient for heating your room or home.