The U.S. Energy Information Administration reports that residential energy consumption per household has decreased over the last 30 years. Improvements in building insulation plus more efficient windows, heating and cooling equipment, and major appliances have more than offset the increase in the average size of homes and the dramatic rise in the use of consumer electronics.

The EIA's most recent (2009) Residential Energy Consumption Survey details this shift in how energy is consumed in homes. It found that heating and cooling no longer account for the majority of home energy use, down from 58 percent of home energy consumption in 1993 to 48 percent in 2009. Making up the difference is the growth in energy consumption for consumer electronics and appliances (including refrigerators), up from 24 percent in 1993 to 35 percent in 2009.

More specifically, the survey found that space heating accounted for the largest share (42 percent) of energy usage in homes, followed by electronics, lighting, and appliances (30 percent), water heating (18 percent), air conditioning (6 percent), and refrigeration (5 percent).

Residential Energy Usage, 2009


Home energy consumption is responsible for a major fraction of the average American's carbon emissions -- roughly 32 percent, according to the Union of Concerned Scientists -- and offers significant opportunities for greater efficiencies. The first step in making our homes more efficienct is to get some answers to basic questions about our energy consumption. How much energy do I use right now. How is that energy produced? What is the environmental impact of the energy I use? What can I do to make a difference?

Start by becoming familiar with the information contained in your natural gas and electric bills and then track your energy usage from month to month. This will make you more aware of just how much energy your home is consuming and more conscious of energy issues generally. It can also provide a big incentive to test various strategies to improve your home's energy efficiency and will help you monitor the impact of those changes.

Understanding Your Gas Bill
The "meter reading" section of the typical gas bill reports the amount of gas used during the current billing period. This is often reported in terms of hundreds of cubic feet (CCF). The volume of gas used is converted from cubic feet into therms, a measure of the heat, or energy content, of the gas. (One hundred CF of natural gas is roughly equal to one therm.) The number of therms then serves as the basis for calculating the various charges on the bill.

(A detailed discussion of the components of a Nicor Gas bill is available here.)

How do you know whether the number of therms you used is "reasonable"? The answer to this is . . . it depends. It depends on how cold it was outside.

Your gas bill may give you this information if it reports the total number of degree days in that billing period. Or you can find degree day records for your area on Weather Underground. (To get started, go to the History Data section and enter your location and a date for which you want weather data.)

    Degree days are used to calculate the effect of outside air temperature on building energy consumption. Heating degree days (HDDs) are a measure that indicates how much colder the outside average temperature was compared to a baseline temperature of 65°F. (This baseline reflects the observation that houses generally require heating if the outside temperature is lower than 65°.) If the average of the high and low temperatures for a particular day was 35°, that would add 30 HDDs to the total for the billing period.

    Similarly, cooling degree days (CDDs) are a measure of how much warmer the outside average temperature was than 65°F.

Dividing the number of therms used by the total number of degree days for that period provides useful information about the energy performance of your house. It reflects the temperature setting of your thermostat, the tightness of your house, and the efficiency of your home's heating system.

With this calculation, you can compare your energy consumption from month to month, and year to year, despite variations in the weather and the fluctuating cost of energy.

(The number of therms used also reflects the energy consumed in heating water and any cooking done with gas. Your summer gas bill will give you a rough idea of how much these uses contribute to your energy consumption year-round.)

Understanding Your Electric Bill
Electrical usage is measured in kilowatt-hours (kWh). (One kWh is equal to using a 100-watt light bulb for 10 hours.) In addition to reporting the number of kilowatt-hours of electricity used in the current billing period, the typical electric bill also provides information showing the customer's usage history to assist in identifying those months in which to expect higher bills and to help homeowners see where lifestyle changes might be made to decrease consumption.

Most consumers pay a fixed per-kWh rate for their electricity no matter what time of day or which day they use it. In some areas, however, consumers may choose an alternative system called Real Time Pricing (RTP) and pay a rate based on the wholesale market price of power, which varies from hour to hour and day to day.

    For much of the day, the "real time" price is lower than the standard fixed price, but at times of peak demand--on steamy afternoons in summer, for example--the price of electricity can soar. RTP customers can save money by reducing their electrical usage during these high-demand hours. (Participants in ComEd's RTP program, for example, have saved on average more than 15 percent on the electricity supply portion of their bills since the program began in 2007.) For the utility, lower peak demand decreases the need to operate more expensive "peaker" plants (to supplement the power from less expensive base load plants), reduces the risk of blackouts, and delays the need to build new power plants.

Another rate structure that rewards customers who cut usage during peak periods is Time of Use (TOU) pricing. With this system, the utility company establishes two or more tiers of prices, setting peak and off-peak rates for different times of the day, days of the week, and seasons of the year. During winter months, for example, the peak period may be early morning and early evening whereas in summer months, it may be midday through early evening, reflecting air conditioning usage. The higher rate charged during peak periods encourages customers to shift usage to off-peak hours.

(A discussion of the components of a ComEd bill and the utility company's various energy-saving programs is available here.)

Most of the energy consumed in homes is produced by burning fossil fuels like coal, oil, and natural gas. When burned, each of these fossil fuels emits various greenhouse gases, principally carbon dioxide (CO2). But they differ significantly in the level of emissions that each gives off.
  • Coal-burning accounts for about one-third of the country's total CO2 emissions and is the single largest source of some of the worst air pollutants, including deadly particulate matter, acid-rain-forming sulfur dioxide, and toxic mercury.
  • Oil burns cleaner than coal but still produces large quantities of CO2 for each unit of energy produced.
  • Natural gas is the cleanest fossil fuel. Burning natural gas does release CO2 and other pollutants but at much lower levels than other fossil fuels. It emits half as much CO2 as coal per unit of energy produced and nearly 40 percent less CO2 than oil.

Close to three-fourths (72 percent) of the carbon emissions related to operating a home is attributable to the electricity used in the home. This is due in part to the relative inefficiency of most power plants in converting the energy in the fuel they burn into electricity. It typically takes three or four units of fuel to produce and deliver one unit of electricity.

The other factor is the electric power industry's heavy reliance on fossil fuels--carbon-intensive coal in particular. Two-thirds of the electricity generated in the U.S. in 2011 was produced by burning fossil fuels, with 42 percent coming from coal, 25 percent from natural gas, and a small percentage from oil. Non-fossil fuel sources accounted for the rest: 19 percent from nuclear power, 8 percent from hydropower, 3 percent from wind power, and the remainder from other renewable sources.

To answer that question, you will need 12 months of data about the energy used in your home. If you do not have a year's worth of utility bills at hand, you should be able to obtain your account history from your local utility companies.
  • To calculate the impact of the electricity you use, add up the number of kilowatt-hours (kWh) of electricity delivered to your house over a 12-month period. Then use the EPA's Power Profiler to find out how many pounds of emissions--such as CO2--are attributable to your annual electrical usage.

    The emissions released in generating electricity vary from one part of the country to another, depending on the types of fuels used in the power plants in each region. Most regions are quite large, encompassing several states. The resulting emissions profile for a particular grid subregion can be surprising. Northern Illinois, for example, is known as a leading producer of nuclear power, a "clean" energy source. But it is part of a regional transmission network that includes Indiana, Ohio, West Virginia, and parts of several other states. The resource mix for this region of the power grid is 70 percent coal and 24 percent nuclear power. This produces emissions of 1.52 pounds of CO2/kWh of electricity.

    The average electrical consumption for homes in Illinois in 2012 was 9,200 kWh/year. (The U.S. average was 10,800 kWh/year.) Using the CO2 emissions rate for northern Illinois, the average home in the Chicago area produces some 13,980 pounds of CO2/year.

  • To calculate the environmental impact of the natural gas (or other heating fuel) you use, first determine the number of therms of gas (or gallons of propane/oil) used in your home over a 12-month period. Then multiply this number by the appropriate conversion factor to determine the number of pounds of CO2 generated. One therm of natural gas generates 11.7 pounds of CO2; for propane, it is 11 pounds/gallon, and for heating oil, it is 22 pounds/gallon.

    The average natural gas consumption for homes in Illinois in 2009 was 1,025 therms/year, producing about 11,990 pounds of CO2.

For most Americans, driving ranks along with electrical usage at the top of the list of daily pollution-causing activities. (For others, air travel can be the biggest contributor to their greenhouse gas emissions.) The DOE/EPA Fuel Economy website offers tips for getting the best gas mileage from your car, can help you find and compare cars, and explains the information provided on the new fuel economy label. The EPA's Green Vehicle Guide is another helpful resource.

There are lots of things you can do--many of them no-cost or low-cost steps--to cut your energy consumption and reduce your greenhouse gas emissions. Frequently mentioned action steps include the following:

  • Replace five of the most frequently-used incandescent light bulbs in your house with compact fluorescent lights--or LEDs.

  • Seal and weather-strip ducts, doors and windows to keep warm air from leaking into your house in summer and out of your house in winter.

  • Set the temperature of your water heater so the water is no more than 120F.

  • Lower the setting on your thermostat in winter and raise it in summer. Install a programmable thermostat to automatically adjust the setting while you're asleep or away from home.

  • Invest in energy-efficient and water-efficient appliances.

  • Use a power strip to turn off electronic equipment with "instant on" features.

  • Recycle aluminum cans, glass bottles, plastic, newspaper and cardboard.

  • When you buy your next car, choose the most fuel-efficient vehicle that meets your needs.

  • If you have the choice, buy electricity for your home from a Green Power source.

More detailed lists of energy-saving measures can be found at these websites:


Website prepared by Eleanor Revelle.
Last revised: September 2017