A spiral coil heat exchanger consists of a number of horizontal layers of spirally wound, finned tubes connected to vertical manifolds at the inner and outermost turns of each coil. This design has advantages in heat recovery and air-conditioning applications. Two theoretical models to predict the performance of this compact heat exchanger are presented based upon unmixed and mixed air-flow considerations. Results of experimental studies on a laboratory model of the spiral coil heat exchanger agree well with the predicted performance of the theoretical models. Charts of effectiveness vs NTU suitable for design are presented.