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Triangular type pyramid surfaces are made as a new type of heat transfer surface, and its sub-atmospheric pressure pool boiling performance is investigated experimentally. Pure water is cited as a working fluid with liquid height of 25 mm and saturation pressures of 15 kPa and 10 kPa. Triangular type pyramid surfaces have pyramid sizes of 2.5 mm, 5.0 mm and 7.5mm, respectively. Performance of the triangular type pyramid surfaces is compared with square type pyramid surfaces whose pyramids sizes are 2.5 mm and 5.0 mm. Heat transfer performance of the triangular type pyramid surface with size of 2.5 mm is the highest among them for both saturation pressures. Heat transfer performance for triangular type pyramid surfaces with real surface area basis is higher by about 1.5 times for size of 2.5 mm, and higher by about 1.2 times for size of 5.0 mm compared with the smooth surface at 15 kPa, and higher by about 1.7 times for size of 2.5 mm, and higher by about 1.3 times for size of 5.0 mm at 10 kPa. When comparing the heat transfer performance of triangular type pyramid surfaces with the square type pyramid surfaces, the triangular type pyramid surfaces have higher performance than the square type pyramid surfaces. Observation of bubbles generated from pyramid surfaces is also conducted for pyramid surfaces with size of 2.5 mm, as well as measurement of bubble growth rates and bubble release times. The results qualitatively show that triangular type pyramid surfaces have good bubble foaming characteristics than the square type pyramid surface. [ABSTRACT FROM AUTHOR]