Missing data for a particular question or item is called item nonresponse. It occurs when a respondent fails to provide an answer to a required item. The ACS also considers invalid answers as item nonresponse. The Census Bureau uses imputation methods that either use rules to determine acceptable answers or use answers from similar housing units or people who provided the item information. One type of imputation, allocation, involves using statistical procedures, such as within-household or nearest neighbor matrices populated by donors, to impute for missing values.

The data on house heating fuel were obtained from Housing Question 10 in the 2009 American Community Survey. The question was asked at occupied housing units. The data show the type of fuel used most to heat the house, apartment, or mobile home. House heating fuel provides information on energy supply and consumption. These data are used by planners to identify the types of fuel used in certain areas and the consequences this usage may have on the area. The data also serve to aid in forecasting the need for future energy needs and power facilities such as generating plants, long distance pipelines for oil or natural gas, and long distance transmission lines for electricity.

House heating fuel is categorized on the ACS questionnaire as follows:

• Utility Gas - This category includes gas piped through underground pipes from a central system to serve the neighborhood.
• Bottled, Tank, or LP Gas - This category includes liquid propane gas stored in bottles or tanks that are refilled or exchanged when empty.
• Electricity - This category includes electricity that is generally supplied by means of above or underground electric power lines.
• Fuel Oil, Kerosene, etc. - This category includes fuel oil, kerosene, gasoline, alcohol, and other combustible liquids.
• Coal or Coke - This category includes coal or coke that is usually distributed by truck.
• Wood - This category includes purchased wood, wood cut by household members on their property or elsewhere, driftwood, sawmill or construction scraps, or the like.
• Solar Energy - This category includes heat provided by sunlight that is collected, stored, and actively distributed to most of the rooms.
• Other Fuel - This category includes all other fuels not specified elsewhere.
• No Fuel Used - This category includes units that do not use any fuel or that do not have heating equipment.