| Value | Category |
|---|---|
| NIU (not in universe) | |
| 1 | No fuel used |
| 2 | Utility gas from underground pipes serving neighborhood |
| 3 | Bottled, tank, or liquefied petroleum gas |
| 4 | Electricity |
| 5 | Fuel oil, kerosene, other liquid fuels |
| 6 | Coal or coke |
| 7 | Wood |
| 8 | Solar energy |
| 9 | Other |