Extinction limits and combustion temperatures in heat-recirculating excess enthalpy reactors employing both gas-phase and catalytic reaction bave been examined previously, with an emphasis Reynolds number (Re) effects and possible application to microscale combustion devices. However, Re is not the only parameter needed to characterize reactor operation. In particular, the use of a fixed reactor size implies that residence time (thus Damköhler (Da), the ratio of residence to chemical time scales) and Re cannot be adjusted independently. To remedy this situation, in this work geometrically similar reactors of different physical sizes were tested with the aim of independently determining the effects of Re and Da. It is found that the difference between catalytic and non-catalytic combustion limits narrow as scale decreases. Moreover, to assess the importance of wall thermal conductivity, reactors of varying wall thickness were studied; results were consistent with theoretical predictions. From these results the effect of scale on microscale reactor performance and implications for practical microcombustion devices are discussed.