How to Calculate a House's Electrical Load in Excel Spreadsheets
By David Miller
The electrical load of a home basically tells you how much electricity your home is using. This is an approximation of your usage, not an exact number. The exact amount can only be determined through metering your electric, which is what your utility company does. One of the easiest ways to calculate this usage is using an Excel spreadsheet. By preparing this spreadsheet you will become more aware of possible energy leaks or places to save energy in the future.
Start Excel, which will open with a new spreadsheet in front of you. If you have never used Excel, it may look overwhelming. Don’t worry; looks can be deceiving.
In column A row 1, type the name of a room in your house. Under the name of the room, type in all the electrical appliances and devices plugged into this room. Continue to list the rooms with the devices down column A until you have everything listed. Don’t forget to list any exterior loads, such as spotlights or porch lamps.
Select cell C1 by moving your mouse to the cell and clicking the left mouse button. Type “Watts” in the cell for the column heading.
Go down the list and type in the watts used by the appliances or devices listed in step 2. Use an average if needed. If the device only has an amperage listing and not wattage listing, use step 5 to calculate the wattage. Continue down the list until you have a wattage number for each device.
To find the watts, take the amperage and multiply it by 120, which is the voltage for all wall receptacles. The number you come up with is the watts used by the device.
Select a cell below the column that has the watts used, and then click on the Greek letter sigma, which looks like a sideways letter "M" in the toolbar, or press "Alt" + "=." You should now have a dashed line surrounding the watt values you typed in. Press “Enter” and a number should appear. This is the sum of the numbers outlined in the dashed line.
Select cell E1 by moving your mouse to the cell and clicking the left mouse button. Type “Hours” in the cell; this is the column heading. List the amount of time the device was used within a 24-hour period. For example, a lamp you read by at night for 45 minutes would be .75 or a oven to cook for 30 minutes would be .50.
Select cell G1. Type "Kilowatts" as the column heading.
Select the first device's cell in the Kilowatts column. Next to the first device, type the following formula “=(c3*e3)/1000)”. Press “Enter” and you should have a value for the kilowatts used by that device within a 24-hour period.
Select the cells below this column and click on the Greek sigma letter again and you should have a total for kilowatts used within a 24-hour period.
- Use this info for a 30-day period and see how close you are to your electric bill when it is received. If you are way off, you are more than likely calculating or averaging something wrong. If you are close by comparison, take the information and use it to make cost saving adjustments by buying more efficient appliances or turning off devices when not in use. If you only occupy certain rooms when you are home, turn off appliances and devices in rooms that you do not use very often.
- If you are handling electrical devices or looking at appliances, always take caution around outlets and wiring. When calculating watts for large appliances, such as stoves, dryers and furnaces, keep in mind that most use 240 volts instead of 120.
David Miller is a Kentucky-based freelance writer who has written on a variety of subjects for eHow. He has also written content for many websites and small businesses. He has a background in the technology sector which he still pursues and enjoys.