How long does a 40 pound bag of wood pellets last?

Typically the heat value is 8700 BTU per pound. This is for a premium pellet at less than 7% moisture. So, about 348,000 BTU per bag. Rule of thumb, I go with 8500 BTU per pound, as not all manufacturers can guarantee Moisture after it is delivered to the Retail sector. Pellets can pick up additional moisture if not stored properly!