By “cleaner,” we mean less ash or maybe a higher efficiency. So, let’s define a couple of terms first.
Ashes: The quality of the wood, the moisture content, and the wood species will all affect the amount of ash from burning cordwood.
On the other hand, pellets are a manufactured fuel. Since the moisture content is strictly controlled, there is very little ash compared to a wood-burning stove.
Combustion efficiency: is measured in a percentage of how well the appliance converts wood into useable heat. It doesn’t reflect how much useable heat is transferred to the home.
Overall efficiency : is the percentage of heat transferred to the living space when a load of fuel, either wood or pellets, is burned. The overall efficiency considers several factors and is a more realistic measurement than combustion efficiency. Combustion efficiencies are often listed in the literature because this is the higher of the two calculated numbers.
Most pellet stoves operate with an overall efficiency rating in the low to mid 80% range. In contrast, many EPA-compliant wood-burning stoves will run a bit lower, in the low to mid 70%.