Patented Fuel is THE HEART OF THE FIRE At the heart of the new way to experience fire is Fire Designs' patented hearth fuel. Hearth fuel is a brand new, unique, proprietary fuel produced from a completely renewable fuel source -- corn. Simply pour hearth fuel into the 64-ounce outdoor hearth burn chamber and light. This 4-Pack case contains: 4 gallons of Hearth Fuel. Each Gallon will burn for approximately three hours.