I think this depends on how much wood you put into it! It takes around 40 minutes for logs to become fully alight so you can estimate four or five hours’ worth before needing another one. You should also remember that your first log may take longer than normal as they tend to smolder more than subsequent ones. After starting out with freshly cut greenwood which has a high moisture content, the logs should dry out after about 30 days so their burning time improves greatly over time. If you want them to blaze away quickly, you can split the logs in half before burning, but this will reduce their burn time.