Geothermal Risks, Barriers, Opportunities
Geothermal heat pumps are one option to provide energy for home heating. Only a few feet underground, the temperature is constant throughout the year (~40-50°F in most parts of the U.S.). If the air temperature is colder than the ground temperature, then it is possible to extract that energy from the ground and use it to heat your house. Likewise, if the air temperature is warmer than the ground temperature, then it is possible to remove that heat from the air and put it into the ground. Heat pumps require some electricity to operate (~1 kWh per 3-4 kWh for heating or 2-3 kWh for cooling), and if you live in colder climates, you probably will want a secondary heat source to ensure your home stays at a comfortable temperature. You also need a home with sufficient acreage in which to place the heat pump coils.
Household-scale Firewood and Pellets
Wood is a viable option for home heating. Wood heating options are either space heaters, which heat the air in a room, such as wood stoves and pellet stoves, or central heaters, such as wood/pellet boilers. Space heaters are most efficient at heating individual rooms or interconnected rooms, and may not efficiently heat an entire house as heat is transferred through the air inside the house instead of through ducts. Central heaters either transfer heat through air ducts or hydronic heating (transfer of heat in water or steam using in-floor or radiators). The type of heating system you have will determine the format of the wood you can use, whether split wood, chips, or pellets. Modern wood and pellet stoves and boilers can be very high efficiency (~70-85%) but require dry wood in order to achieve those efficiencies. One downside of wood-based heating compared to natural gas or propane is the higher maintenance requirements. Wood or pellet heating requires routine loading of the firebox or the hopper with wood or pellets and cleaning and disposal of the ash. Unlike wood stoves, which are loaded manually, pellet stoves are loaded from a hopper using an auger. Although pellets are more expensive than split wood, the automation makes pellet stoves more convenient for loading the wood, though it also means they require some electricity to operate. The EPA has a database that allows you to compare wood and pellet stoves and boilers based on their heat output, environmental performance, and efficiency.