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Changes in Energy Usage in Residential Housing Units

Over the 19 years since the first RECS in 1978, the number of households in the United States has increased by 33 percent from 76.6 million to 101.5 million in 1997. While each of the four main Census regions have shared in this growth, the rate has differed from region to region. The largest increases were in the West and South, where the number of households grew by 56 percent and 46 percent, respectively. In the Northeast the number grew by 13 percent and in the Midwest by 17 percent.

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Although the number of households in all four U.S. Census regions has increased over the past 19 years, the distribution of those same households across the Nation has changed dramatically. The change in the distribution directly affects both the types and the amounts of fuel consumed in the United States In the South the proportion of households has increased from 32 percent in 1978 to 35 percent in 1997. At the same time, households in the West increased from 18 percent to 22 percent.   In contrast, the proportion of households in the Northeast and the Midwest decreased by 4 percentage points and 3 percentage points, respectively.

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Over the past 19 years, the size of housing units in the United States has become increasingly larger, resulting in an increased demand for energy-consuming activities such as heating, air-conditioning, and lighting. The proportion of smaller housing units, those with four or fewer rooms (excluding bathrooms), has decreased from 35 percent to 30 percent. At the other end of the scale, the proportion of larger housing units, those with seven or more rooms, has increased from 22 percent in 1978 to 29 percent in 1997.

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The total amount of energy consumed by American housing units in 1997 was 10.2 quadrillion Btu. In 1978, 10.6 quadrillion Btu had been consumed. (Those totals are not statistically different.) Over this 19-year period, the total Btu consumption first decreased by 19 percent over the 1978-1982 period, then reversed course and increased by 19 percent over the 1984-1997 period.

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Total Site Energy Consumption per U.S. Housing Unit

On a per-housing unit basis, energy consumption was 27 percent lower in 1997 than in 1978, dropping from 138 million Btu per housing unit to 101 million Btu per housing unit. All of this decrease occurred in the 1978-1987 period. Btu consumption per housing unit in 1997 was unchanged from the 1987 estimate.

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Percent of Total U.S. Residential Site Energy Consumption
by Fuel

Over the past two decades, the sources of the energy consumed in U.S. housing units has changed. The percentage of energy provided by electricity increased from 23 percent of all energy consumed in 1978 to 35 percent in 1997. In contrast, the energy provided by fuel oil/kerosene (some housing units use either fuel oil or kerosene; some use both) decreased from 21 percent in 1978 to 10 percent in 1997. The percentage of energy provided by natural gas, 52 percent in 1997, and LPG, 4 percent in 1997, were statistically unchanged from the 1978 levels.

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Percent of Total U.S. Residential Site Energy Consumption by End Use

The end-use consumption of energy in U.S. housing units has changed over the 1978-1997 period. Energy consumption for space heating decreased from 66 percent of all Btu in 1978 to 51 percent in 1997. Btu consumption for appliances and lighting increased from 17 percent of all Btu in 1978 to 27 percent in 1997. Over the same 19-year period, the proportion of Btu consumed for cooling remained unchanged. The proportion of Btu consumed for water heating increased from 15 percent in 1978 to 19 percent in 1997.

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Site Energy Consumption per U.S. Housing Unit by Total and End Use

Energy consumption per housing unit has decreased by 27 percent since 1978, when an average 138 million Btu were consumed, to 1997, when an average 101 million Btu were consumed. Virtually all of that decrease was the result of a 44-percent decrease in Btu consumption for space heating. In 1978, an average of 91 million Btu was consumed for space heating (66 percent of all the Btu consumed); in 1997, an average of 51 million Btu (51 percent of all the Btu consumed) was consumed for space heating.

Somewhat offsetting the large decrease in Btu consumption for space heating was a 17-percent increase in Btu consumption by appliances and lighting from 23 million Btu per in 1978 (17 percent of all the Btu consumed) to 27 million Btu per in 1997 (27 percent of all the Btu consumed).

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Percent of U.S. Residential Space-Heating Site Energy Consumption by Main Heating Fuel

In addition to an overall decrease in energy consumption for space heating, the source of the space heating Btu changed substantially over the 1979-1997 period. While the percent of all space heating Btu from natural gas increased from 61 percent in 1978 to 70 percent in 1997, the percent provided by fuel oil/kerosene dropped from 30 percent in 1978 to 18 percent in 1997.

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Space-Heating Site Energy Consumption per U.S. Housing Unit

On a per-housing unit basis, the decrease in Btu consumption for space-heating occurred regardless of the main heating fuel used. On a percentage basis, the largest decrease in space heating energy consumption occurred in those housing units whose main heating fuel was electricity. In those housing units, Btu consumption decreased by 60 percent, from 32 million Btu per in 1978 to 13 million Btu in 1997. Btu consumption in housing units where natural gas or fuel oil/kerosene was the main heating fuel decreased by 34 percent and 33 percent, respectively, over the 1978-1997 period. Btu consumption in housing units where LPG was the main heating fuel decreased by 21 percent over the same period.

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Main Heating Fuels

Since 1978, the percentage of households using electricity as their main heating fuel has nearly doubled, from 16 percent in 1978 to 30 percent in 1997. Nevertheless, natural gas remained the most frequently used main heating fuel, used by 55 percent of households in 1978 and 52 percent in 1997, with little change over the 19-year period. Over the same period, the percentage of households mainly using fuel oil or kerosene for space heat decreased from 22 percent to 10 percent.

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Main Central Heating Systems

In 1978, when the first RECS was conducted, 69 percent of U.S. housing units main source of heat was some type of central heating system; either a warm-air furnace, a steam or hot-water system, or a heat pump. By 1997, the percentage of housing units whose main source of heat was a central heating system was 78 percent.

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Types of Main Central Heating Systems

Warm-air furnaces are the most frequently used main central heating system, followed by steam and hot water systems and heat pumps. In 1978, heat pumps, used in only 2 percent of all housing units, were relatively rare. By 1997, the use of heat pumps had quintupled to 10 percent of housing units. Since 1978, the use of warm-air furnaces has increased by 5 percentage points, and the use of steam or hot-water systems has declined by 5 percentage points.

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Secondary Heating Equipment

As the name implies, secondary heating equipment is that which supplements main heating systems. In 1978, 30 percent of all households used secondary heating equipment, compared with 39 percent in 1987. In 1997, 34 percent used secondary equipment, 5 percentage points lower than in 1987 but 4 percentage points higher than in 1978.

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Secondary Heating Fuels

Secondary heating fuels are used as supplements to a household’s main heating fuel. Some households use more than one. In 1978, wood was the most commonly-used secondary heating fuel.  By 1997, electricity had caught up to it.   Meanwhile, the other measurable secondary heating fuels, natural gas, fuel oil/kerosene and LPG, stayed at lower levels throughout the period.

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Types of Air-Conditioning Equipment

In 1978, 56 percent of U.S. households used air conditioners of some kind. By 1997, the use of air-conditioning equipment had increased to 73 percent. This overall increase was the result of a very large increase in the use of central air-conditioning systems that more than offset a decline in the use of window/wall units. In 1978, the use of window/wall units exceeded the use of central systems by 10 percentage points (33 percent compared to 23 percent). By 1987, the percent of households using central systems, 34 percent, surpassed the percent of households using window/wall units, 31 percent. The trend continued through 1997, when there were nearly twice as many central systems as window/wall units in use (47 percent compared to 26 percent).

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Geographic Location of Central Air-Conditioning Equipment

Over the past 19 years, the four Census regions have experienced dramatic growth in the use of central air-conditioning equipment. As would be expected with its warm climate, the South consistently had the highest percentage of households using central air-conditioners, followed by the Midwest, the West, and the Northeast.

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Appliances

The 19 years covered by the RECS have seen continuous and large increases in appliance use in U.S. households. Microwave ovens, which were introduced in the mid-1970’s, were found in only 8 percent of households in 1978. By 1997, the percentage of households with a microwave oven has increased by a factor of more than 10 to 83 percent. The use of dishwashers has increased from 35 percent in 1978 to 50 percent in 1997. Water bed heaters, which were not counted in 1978, reached their peak of 15 percent (the data point is not shown) of all households in 1990. Their use has since declined to 8 percent of households in 1997. Although the use of clothes washers has remained about the same over the past 19 years, the use of clothes dryers has increased. In 1978, 59 percent of households used a clothes dryer, compared with 71 percent in 1997. The percentage of households using a stand-alone freezer has remained essentially unchanged over the past two decades.