numbers you should know

Do you want to have some idea about your carbon footprint? You can look at your energy bills but most people do not have all those in one place. Furthermore there are often many sources of energy that we use and all are billed by different parties. And to make it even more complicated, all are expressed in different units that are often quite confusing.

There are numerous online calculators that can estimate your energy use and your CO2 production, but after you try one of these you wonder, what do I do now ? Or maybe you just don't care. But just in case, here are some practical guidelines based on common averages. If you keep these in mind you can really watch what you do day to day. And that can make a difference.

Electricity it turns out is one of the easiest to remember. It is expressed in kWh or kilowatt-hours. A kilo watt is 1,000 watts and a kWh is anything using 1,000W that stays on for a full hour. Nearly all electrical devices have stickers with power ratings expressed in W. It will read something like 120V, 60Hz, and 100W. The W is the important number.

And here is an easy rule of thumb that is both handy and reasonably accurate. Every 100W device that stays on for 24 hours uses 2.4 kWh. If it stays on all year that will cost you about $100 per year. On average it will also produce 1,100 pounds of CO2 per year -more if you have dirty coal-based electricity and less if your power company uses solar or wind.

100W = 1,100 pounds/year

or

$1 spent on electric = 11 pounds

Every gallon of gas for your car produces 20 pounds of CO2 and if you have a 15 gallon tank, that is 300 pounds per fill-up. If you gas up once a week that will total 15,600 pounds of CO2 per year. That is equivalent to nearly 1500W of electric power or an electric space heater or hair dryer running 24h per day, 7 days a week, 365 days a year.

If your car gets 20 mpg -the average US passenger car gets 21.5 mpg- then you produce one pound of CO2 for every mile you drive. The average passenger car in the US, driven for the average distance produces 11,500 pounds. The "average" light truck produces 16,000 pounds.

CAR = 1 pound/mile

Natural gas is usually expressed in Therms on your bill. A therm is 100,000 Btu. Burning a therm of natural gas produces roughly 12 pounds of CO2. If you use 0.5 therm per day you will spit out almost 2,200 pounds of CO2 per year. 0.5 therms per day is common for households with a water heater and a gas range.

WATER HEATER = 2,000 pounds/year

Propane is just a bit dirtier than natural gas. It produces 14 pounds of CO2 per therm. So for the same amount of heating you would be producing 2,555 pounds of CO2. Fuel oil is even dirtier. It produces 16 pounds per therm. For equivalent heating, fuel oil produces almost 3,000 pounds of CO2.

But the worst offenders are the cozy, heart-warming fire-places burning wood. Or barbecues using charcoal. Wood produces 3,814 pounds of CO2 per short ton (2,000 pounds). That is 22.2 pounds per therm. That is just slightly better than coal at 22.7 pounds per therm. Burning municipal solid waste is slightly less dirty at about 19 pounds per therm.

WOOD = 1.9 pounds per pound
(if you wonder how 1 pound can produce 1.9 pounds, don't forget that you add oxygen from the air when you burn something. Oxygen is heavier than carbon)

These guidelines only express CO2 produced, not total pollution. Apart from CO2, burning fossil fuels also produce other pollutants. Some of these are gaseous and others are particles. And once again, coal and wood are some of the dirtiest fuels you can use.

Some might argue that wood is better because you are just releasing carbon that was captured from the atmosphere recently, not carbon that was stored millions of years ago. The same argument is often used for other ethanol and other biofuels. This is a feel-good argument that is largely irrelevant however. What matters is how much absolute CO2 we produce, not how efficient we are.