Feng Shui is based on the concept that every physical object has an electromagnetic field around it that influence and interact with each other. It helps in creating a positive energy field all around by eliminating the negative ones.
It is based on the belief that if there is any negativity around us it influences our mood and lifestyle. As vaastu is based on directions, Feng Shui deals with chi energies. It also covers interior decoration to a greater extent.
It is very important to apply Feng Shui and Vaastu in harmony as Feng Shui originated for different place and weather.