| CNPI | Coal Non-Professionally Installed |
| CPI | Coal Professionally Installed |
| E | Electric |
| F | Electric Portable Heater |
| FIREPLACE | Fireplace |
| FLOORFURN | Floor Furnace |
| Y | Geothermal |
| HEATPUMP | Heat Pump |
| K | Kerosene |
| H | Kerosene Portable Heater |
| L | Liquid Propane Gas |
| M | Liquid Propane Portable Heater |
| G | Natural Gas |
| NONE | None |
| O | Oil |
| OT | Other |
| PELLETSTOV | Pellet Stove |
| T | Solar Non-Professionally Installed |
| S | Solar Professionally Installed |
| WALLUNIT | Wall Unit |
| X | Wood Non-Professionally Installed |
| W | Wood Professionally Installed |