Appliance Types and Policy Goals
A. Pellet Stoves
In many ways the pellet stove represents the pinnacle of innovation in residential wood combustion because it blends traditional wood heat with automation and convenience. This appliance and its unique fuel were invented in America in the early 1980’s. Pellets revolutionized wood fuel by densifying the wood in order to make it more efficient to transport. Furthermore, the uniformity in size and low moisture content of the fuel, combined with the automated combustion system removed much of the user error associated with traditional wood burning.
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Pellet stoves tend to be more efficient than cordwood stoves because they use a low moisture fuel and automatic controls maintain a more ideal combustion environment, which produces fewer emissions per unit of heat output as compared to a conventional wood stove. The stove self-regulates by feeding a pre-determined amount of fuel and air to the stove over time to maintain a constant temperature and efficient burn. While the fuel intake and temperature are automated, the maintenance often is not, requiring periodic ash removal and cleaning. Pellet stoves also require a small amount of electricity to power their blower fans and automated hopper.
This creates a small monthly electrical bill and leaves the stove vulnerable to power outages. Pellet stoves approved for use in Washington state range in emissions from 0.5 to 4.4 g/hr with over 70% of them at 2 g/hr or lower. There are higher emitting pellet stoves in production, but since pellet stoves are not required by the EPA to undergo testing, there is no comprehensive list of the pellet stoves that exceed Washington’s standard of 4.5 g/hr. Pellet stoves range in price from $1,200-$4,000+.
Pelletized fuel can be purchased in easy-to-handle bags, which can be fed into a hopper on the stove unit or in bulk delivery to a storage bin attached to a home. Pellets cost $250 per ton on average, comparable in price to natural gas and cheaper than most other fossil fuels. Aside from pelletized wood, many stoves are designed as multi-source fuel appliances, which can burn other forms of biomass such as pelletized grass, corn, cherry pits, etc. The pellet industry is currently moving forward on establishing a consistent set of pellet standards, which will do much to guarantee a consistent burn in stoves.
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Figure 27: Pellet Stove Diagram
Policy Considerations
Due to the relatively low, consistent emissions of pellet stoves, they are well suited for suburban and even urban environments that often have more air quality issues than rural areas. European countries have long provided a range of incentives to pellet stoves and boilers and many believe it is only a matter of time before the US and individual states do the same. Particularly in the Northeastern US, there are obvious opportunities to encourage a switch from fuel oil or propane to pellet fuel as a primary or secondary heating source. Many changeout programs in air quality non-attainment areas already provide a greater incentive to switch from an older, non-certified wood stove to a pellet stove, and programs focusing on urban areas should consider providing greater benefits to those purchasing pellet stoves to encourage adoption of the cleanest burning appliances in these areas. Another factor that should be noted is that the pellet industry is relatively new and so not all areas have access to bulk delivery services. To counter this, some incentive programs are designed specifically to assist the pellet fuel industry in building a stronger bulk fuel distribution network, such as the program in New Hampshire discussed in the rebate section of chapter 5.
Since pellet stoves require purchasing fuel (unlike self-harvested cord wood), they are not as well suited for rural, low-income households. Incentive programs should take this price difference between pellets and cordwood into account when designing the program.