The duration a 20 lb propane tank lasts depends on the appliance’s BTU (British Thermal Unit) rating and usage. On average, it might last around 18-20 hours when used with a standard propane grill with a burner that produces 30,000 BTUs per hour. However, this can vary significantly based on factors such as the size and efficiency of the appliance, the weather conditions, and the level of propane in the tank. To get a more accurate estimate, check the appliance’s BTU rating and compare it to the propane tank’s capacity. Keep in mind that running multiple appliances simultaneously or using them for extended periods will deplete the propane more quickly.