Down jackets don't need to be washed too often, since frequent washing makes the down lose its fluffiness. Instead, make a habit of airing it and spray with Clothing Mist once in a while.
Using an enzyme-based detergent when you wash will dissolve the natural oils and the jacket will lose some of it’s insulation abilities. Instead, use an enzyme-free detergent like Steamery Delicate Wash. Rinse out all detergent residues and tumble dry, inside out, on low temperature. Add three or more clean tennis balls to the tumble dryer and let the program run until your jacket has dried completely. Pause to shake the jacket once in a while, you want the down to spread evenly throughout the garment. The drying is done and the jacket is ready to wear when it’s completely dry and has a fresh smell to it.