The orifice pulse tube refrigerator has the potential to become a small, reliable cryocooler. In linear approximation the refrigeration produced is due to two independent contributions: an enthalpy flow in the bulk of the gas and an enthalpy flow due to heat exchange with the wall. These effects are treated independently in the literature. For pulse tube operation they can be of the same order of magnitude and have to be combined. Experimental verification is obscured by the regenerator loss, which is difficult to determine accurately. By performing experiments at room temperature this loss can be made negligible. These experiments are in agreement with the theory.