How efficient are pellet stove and inserts?

The literature for most pellet stoves and inserts today list efficiencies in the range of the low 70% to the low 80% range.  Because of the fine ash when burning pellets, it is very important to clean the stove on a regular basis.  This ash collects on the heat exchange tubes and other surfaces in the firebox.  This will impede the heat transfer to the steel and will affect the heat output and efficiency of the stove.  So, always follow the recommendations for routine maintenance by the manufacturer.  It’s laid out step by step in your owner’s manual.