A ceiling fan should only be flush mounted if it was manufactured with this option. Some people create a DIY flush mount by removing the electrical box or downrod. Removing the downrod can decrease stability and put the fan at risk of falling. Installing a fan flush mount that the manufacturer did not design to sit close to the ceiling can cause the blades to overheat or in the worst case, start a fire. However, you may be able to safely install the fan closer to the ceiling by removing the fan light kit from the assembly. You would then need another source of lighting for the room.