In this paper a reconstruction method is presented, which allows the calculation of three-dimensional temperature and velocity fields in an industrial furnace by measuring the propagation times of sound waves. Transceiver systems working in a coal fired power station and reconstructing two-dimensional fields are well known. Referring to these real conditions, the idea was to use two measurement planes situated over each other and projecting the fields in the volume between them. Some simulations show that weak inhomogeneous fields can be well reconstructed, whereas in the presence of turbulent flow and noise a reconstruction is critical.