Republished: July 15, 2013: To correct an error in the text. Thirty percent of new home starts in 2012 were in apartment buildings with five or more units, the highest percentage since 1986 and up sharply from 18% in 2009 and 2010, according to the U.S. Census Bureau. About 17% of households (19 million) lived in apartment buildings with five or more units in 2009, up from 13% (11 million) in 1980, but they only accounted for 9% of home energy use in both years. Over the same period, single-family homes maintained a steady share of total households, but their share of total home energy use went up. Apartments in smaller buildings have declined as a share of both households and energy use, and mobile homes remain a small segment of the residential sector. Households in apartment buildings with five or more units use much less energy than the average for all households, and those in newer units use even less energy than those in older ones. As recent new construction joins the housing stock and older buildings fall out, energy use per household in large apartment buildings likely will continue to decline.

Households living in apartment buildings with five or more units use about half as much energy as other types of homes. Lower energy use in apartments can be partially explained by their smaller living space. Additionally, apartment units are bordered by other units or common areas on one or more sides and typically have fewer windows, limiting exposure to exterior temperatures. Since 1980, per-household energy use in the larger apartment buildings has fallen by 38%, compared with declines between 15% and 32% for other home types. Energy use per household has decreased across all home types due to efficiency improvements in major equipment and appliances, despite increases in the average size of homes and the use of electronics. Much of this decline in home energy use is attributable to reduced consumption for space heating, as equipment has become more efficient, population has shifted to warmer climates, and many homes now have better insulation and windows. Apartments in buildings with five or more units have seen the largest change in per household energy use for space heating, which fell by 48% between1980 to 2009.

Households in the larger apartment buildings in 1980 consumed almost as much energy for space heating (42 million Btu) as is now used for all purposes (a total of 46 million Btu for space heating, water heating, air conditioning, and appliances in 2009).portable ac units for indoors Another way to examine household energy data is to look at energy use for a single year across homes built at different times. ac unit supply air temperatureOverall, new homes consume about as much energy as older ones, but trends differ by home type. ac unit running too longHouseholds living in new (2000s) single-family homes use more energy than those living in older homes. For all other home types, the reverse is true. When comparing newer (2000s) homes to those built in the 1970s, apartments in large buildings show the greatest decrease in per-household energy consumption.

Households in large apartment buildings constructed in the 2000s consume 12% less energy than those built in the 1970s. Less energy is used by households in new apartments despite having more energy-consuming devices than older apartments—more air conditioning equipment, more major appliances like dishwashers and clothes washers and dryers, and more consumer electronics like computers and televisions. The comparisons of energy use in this article are based on the amount of energy delivered to residences, and do not include energy losses in the generation of electricity that is used by households, which is part of the total amount of primary energy required to support site-level energy use.Use this information as a safety guide for choosing, installing and using space heaters in your home. These heaters are fueled by kerosene, natural gas, propane or electricity. All of these heaters can cause fires. Gas and kerosene heaters can cause buildup of carbon monoxide and nitrogen dioxide in your home.

High levels of carbon monoxide can be fatal. Portable kerosene and unvented gas heaters release combustion products directly into your home. Overusing the heater or using an oversized heater can result in elevated levels of carbon monoxide or nitrogen dioxide fumes in the air. These fumes can cause cold or flu-like symptoms, headaches, and eye, nose and throat irritation. Don't use these heaters as your main heat source, even during power failures. Using these heaters for an extended period of time increases the build up of combustion products. A better option is to run a generator outdoors during power failures for heating, refrigeration, etc. Have these heaters inspected and serviced regularly. Follow the manufacturer's advice about use and maintenance, but service the units at least once a year. Use ONLY grade K-1 kerosene. K-2 (even if it looks as clear as K-1) has a higher sulfur content and is used for other purposes. Never add fuel to the heater when it is hot.

The fuel can ignite, burning you and your home. Keep the heater away from things that can burn, such as furniture, rugs or curtains. Follow the manufacturer's advice about placement and use. Choose a heater carefully. Don't choose a heater that is too large for the space you plan to heat. Choose one that won't tip easily and has a fuel gauge to prevent overfilling. Check the wick weekly. Clean it if it's dirty and replace it if it's worn. Store kerosene outdoors, in a container used only for kerosene. Don't use kerosene from a prior heating season as it can change and may not burn properly. Unvented gas heaters do not use a chimney or vent. They are connected to the house fuel supply (natural gas or propane) and may be wall-mounted, free-standing or inserted in a fireplace. Have the heater installed by a professional (such as your gas supplier). ALL gas appliances should be professionally installed. Don't buy an oversized heater (in terms of heat output).

Use the sizing guidelines posted where you buy the heater to choose the correct output. The room size not only determines heating needs, it also affects how much air is available to dilute the combustion products. Vented gas heaters are similar to unvented gas heaters except they are connected to a chimney or other venting system. These heaters must be connected to a chimney or other venting system. As with all gas appliances, have the heater installed by a professional. Check the chimney or flue each fall for any obstructions (such as birds' nests) and clean as needed. Use your heater in accordance with the manufacturer's instructions. Have the heater inspected and serviced at least once a year. Don't use a portable electric heater in rooms with running water (such as a kitchen or bathroom) or in a damp basement, unless connected to ground-fault interruptor circuits. These circuits, also called GFI, automatically shut down when exposed to water or other shock hazards.