Adding ceiling heat registers from the ducts that supply upper rooms is the easiest but least effective way to heat a basement. Zoned heating with registers at floor level or in-floor coils under tiles provides the best comfort. You may be able to add a dedicated basement zone to your existing furnace. If you have the headroom, you also can install a special subfloor such as DriCore that serves as a barrier from damp concrete and helps maintain a healthy and even temperature.