What is the typical high and low temperature difference across a gas furnace?

The typical temperature difference across a gas furnace, known as the temperature rise, generally ranges from 30 to 70 degrees Fahrenheit (about 17 to 39 degrees Celsius). This means that if the incoming air is around 60°F, the output air could be between 90°F and 130°F. The exact difference can vary based on the furnace's efficiency, design, and the specific heating requirements of the space. Proper maintenance and adjustment can help optimize this temperature rise for efficient heating.