Abstract We have investigated a fin-type air heater, both experimentally and theoretically. In the experimental set-up, the fins are integrated with the upper plate of the conventional duct-type air heater with single glazing. The experiments were performed on two clear days for two different mass-flow rates. A transient model is then developed to study the performance of the finned air heater and, by adjusting heat-transfer coefficients, the theoretical data are fitted to the experimental results. Agreement between theoretical predictions and experimental values is found to be good. We have used the resulting values of the heat-transfer coefficient to predict the performance of the system when the fins are placed in the lower metallic plate or in both the upper and lower plates. The dependence of efficiency on fin density has been studied.