Abstract There is a warm groundwater resource on the Bay of Plenty coast of the North Island, New Zealand. Drillholes up to 600 m deep produce water at temperatures of 35–45°C. Downhole temperature measurements in 77 wells and thermal conductivity measurements of representative rock samples are used to determine the vertical conductive heat flow. Sixty-seven percent of the heat flow results are in the range 60–120 mW m −2 (mean value of this group is 88 ± 16 mW m −2). These are consistent with the back arc location of the study area relative to the Taupo Volcanic Zone. In some places heat flow is considerably enhanced (up to 336 mW m −2) due to convective heat transfer which occurs where vertical permeability is large.