For a fire that produces a constant flame, it's important to use hardwood logs as this burn much longer than other types; however, softwoods are better for those who want an intense blaze which only requires stoking every hour or so. In addition, dense woods such as oak and ash can also produce flames that last several hours because they smolder slowly rather than simply collapsing into charcoal after being set alight once more. If you're purchasing your firewood from a professional supplier then make sure to ask them what constitutes their most popular choice – this information should give you some idea about whether or not you should purchase one particular kind over another.