Wood pellets, wood chips, and cord wood - a comparison of biomass fuel types
Not all biomass fuels are created equal. Of the biomass fuels commonly used in the U.S. -- wood pellets, wood chips, and cord wood -- some are more efficient, cheaper, and cleaner than others. Learn more about the various biomass fuels you can use to heat your home
While there are a variety of possible wood fuels, most modern biomass heating devices on the market today burn wood pellets. It is important to use high quality pellets to ensure your device operates most effectively. Learn more about the wood pellet heating systems here.
There are three or four types of solid biomass fuels used for space heating: logs (cord wood), wood chips, and wood pellets. Pellets can be made either from wood, energy crops or agricultural waste. Of these, wood pellets are most commonly used in the U.S, and other cold climate regions. The relatively high heating value of wood pellets, low moisture (between 8% and 10%), and very low ash content (as bark has been removed) make them the most versatile. Also, wood pellets are highly standardized and usually made from one or just a few varieties of wood.
Which is the better fuel?
Typically, the more standardized or homogenized a fuel, the better. Remember, any heating device works in conjunction with the fuel in order to provide the heating you need. If the fuel is standardized (think about how #2 heating oil or natural gas is all pretty much the same), the device too can offer a standardized stream heat (output).
Pellets are more standardized than wood chips, and significantly more standardized than cord wood. One of the main differences is density. Pellets go through industrial processing so that every pellet has very similar mass per volume (measured as lbs per cubic foot, usually 40-46 lbs/ft3) and therefore, uniform density. Some parts of a wood log are naturally denser than others, so it's hard to control the burning rate. Wood chips have similar density issues, but because they are in small pieces, they burn a bit more evenly than cord wood.
With the uniform density of wood pellets, it is easier for the heating system to provide a predictable, even rate of heating over a period of time--a concept referred to as being in "steady state." Systems running at steady state will be more efficient and provide more reliable indoor comfort.
Another critical reason why wood pellets are better is particulate matter (PM) emissions. PM emissions are very important to public health and as such, the EPA regulates the level of acceptable PM emissions from wood-burning systems. Due to standardization and more complete, even burning, pellets are known to have a lower level of PM emissions than wood chips and a much lower level than cord wood. Several state and federal government agencies and their laboratories have done tests to measure emissions from the different form of biomass and pellets are known to generally perform better.
In short, because of density, emission and other factors like moisture and ash content, wood pellets are a more effective form of biomass fuel.
Price-wise, how do pellets compare to cord wood or wood chips?
As discussed above, pellets are more a standardized form of biomass fuel. They are industrially processed and provide for a more reliable heating experience, as compared to cord wood or chips. When looking only at price, pellets tend to be marginally more expensive than cord wood. However, pellets offer great value because they are easier to store and load into the heating system (most new boiler devices have feeder tanks with automatic feeding of pellets). Given that they are less polluting, burn better and easier to handle, the difference in price is often considered negligible.
Finally, some of the best-in-class biomass heating device manufacturers also recommend the use of pellets for performance that gives you the highest efficiency and the lowest emissions. In addition to that, states like Massachusetts only provide rebates for high-efficiency wood pellet heating systems.