The present research is an experimental study of pool boiling behavior using flat, microporous-enhanced square heater surfaces immersed in saturated FC-72. Flush-mounted 2 cm x 2 cm and 5 cm x 5 cm copper surfaces were tested and compared to a 1 cm x 1 cm copper surface that was previously investigated. Heater surface orientation and size effects on pool boiling performance were investigated under increasing and decreasing heat-flux conditions for two different surface microgeometries: plain and microporous coated. Results of the plain surface testing showed that the nucleate boiling performance is dependent on heater orientation. The nucleate boiling curves of the microporous coated surfaces were found to collapse to one curve showing insensitivity to heater orientation. The effects of heater size and orientation angle on CHF were found to be significant for both the plain and microporous coated surfaces.