The gel fuel used in a ventless gel fireplace generally burns for a duration of approximately two to three hours, depending on various factors such as the size of the canisters and the specific model of the fireplace. Larger canisters can provide a longer burn time, while smaller ones may last closer to the two-hour mark. Additionally, the intensity of the flame and the environmental conditions can affect the burn time. For example, a well-ventilated space may allow for a quicker combustion of the fuel. It is important to follow the manufacturer's guidelines regarding fuel usage to ensure optimal performance and safety. For further information about specific models and their fuel requirements, it may be helpful to check the current web page or product details available online.