Comparability — Austria [top]

Liquefied gas is not identified in 2001. The 1991 and 2001 samples identified wood shavings as source; it is combined with wood in FUELHEAT.

Comparability — Botswana [top]

The 2011 sample includes "bio gas" which is categorized as a biofuel.

Comparability — Canada [top]

Bottled gas is explicitly included with "gas".

Comparability — France [top]

Beginning in 1990, households reporting gas from the town network are distinguished from households reporting bottled gas. In all samples, households listing "urban heat," "city heating" or "city gas" are coded to "Unknown," because the fuel used is undocumented.

In 2006, the question was explicitly asked of households in metropolitan France. In 2011, the question was explicitly asked of households in mainland France.

Comparability — Germany [top]

Information on fuel source of the dwelling is only available in the 1987 sample. The 1971 sample asked about type of heating but not the fuel source.

In the 1987 sample, 5% of all households asked the question indicated "remote heating" as a source and are coded into the "other" category. Heating fuel source was also asked of buildings and these do not always correspond with source of heat for the dwelling. Refer to the unharmonized variable to identify the building fuel source.

Comparability — Ireland [top]

The 1981 and 1991 samples ask for the main source of heating in winter. The 2016 sample specifically asks for details of the energy source for central heating.

The 1991 unharmonized source variable has more detail on the "other" fuel sources compared to 1981, which is preserved in unharmozied source variables.

Comparability — Israel [top]

The type of fuel used for the most hours in a day was reported.

Comparability — Italy [top]

The 2001 and 2011 samples contain multiple questions about the source of heating. The households that report more than one heating source were included in the category "multiple sources".

Comparability — Mongolia [top]

The 2010 and 2020 census questions only identify the fuel source for households without a central heating system. A "low pressure stove" is considered to use gas, while a "fire stove" uses some kind of solid fuel.

Comparability — Palestine [top]

The universe differs across samples.

Comparability — Poland [top]

The 1988 and 2002 census question was asked of only dwellings that did not have a collective central heating system. The 1988 sample differentiates between households that have individual central heating that is based on gas or some other type of fuel (which is categorized in "other"), and wood product stoves.

Comparability — Portugal [top]

The census question was asked of only households with a heating system.

Comparability — Puerto Rico [top]

The universe differs across samples.

Comparability — Romania [top]

The universe changes over time. Only dwellings with no central heating were considered in the 1977 sample. In the 1992 and 2002 samples, dwellings without collective central heating are in the universe. If a dwelling had multiple heating systems, only the primary one was recorded. All households provide this information in 2011.

Comparability — Slovenia [top]

The universe does not include households that obtained heat from a plant supplying heat to a city or a large area.

Comparability — Spain [top]

The census question was asked of only households with a heating method.

Comparability — Switzerland [top]

The 2011 census question was asked of all households while in the 1980, 1990, and 2000 it was asked to private households with heating except emergency shelters.

In 2011, the heat pump and district heating are classified respectively as other and multiple sources of heating.

Comparability — United States [top]

Households living in unheated units reported "no fuel used." If a dwelling had multiple heating systems, only the primary one was recorded.

In 1960, only 20% of households were asked the fuel question.

Comparability — Uruguay [top]

The categories differ slightly across samples. The fuel oil category combines the responses "gas oil" and "fuel oil". The 2006 sample was a survey and therefore only enumerates a subset of the population. This sample also does not include a category for "wood", which constituted a sizeable portion of responses in previous years, implying that these cases may be classified in NIU, i.e. without heating.

The 2011 source variable includes "super-gas" as a response category, which is a plant-based fuel technology. It is included in the "Bottled gas, in tank, liquefied" category in the integrated variable.

Comparability — Zambia [top]

The 2010 Zambia enumeration instructions indicate that candles should not be considered a source of energy for heating. Nonetheless, they are indicated in the source and integrated variable.