take a look at

http://www.fpl.fs.fed.us/documnts/te...calculator.pdf


how much pellet wood you consume is a function of how big a fire you're
burning

which is driven by:
size of heated space
indoor temp
building insulation
outdoor conditions

asking "How long does a bag of wood stove pellet last?"

is like asking "How long will a 40 lb bag of dog food last?"

forever if you don't have a dog, not very long if you're running a dog
team everyday

cheers
Bob