The economic losses of heat stress (HS) and the return on investment in cooling systems (CS) in dairy herds are difficult to evaluate. The objective of the present study was to evaluate the effects of HS and the technical and economic impact of CS in 3 different zones of Spain. To estimate the effects of HS, weather records of southern (SO, Sevilla), central (CT, Toledo) and northern (NO, Lugo) Spain were submitted to the HS biological model (production, intake and reproduction) proposed by St. Pierre et al. (2001). The effects of HS and CS were simulated over 5 years in a stochastic dairy farm model (www.dairyfarm.es). One dairy herd for each zone was created with the same technical and economic characteristics: 300 dairy cows with an average milk production of 30.5 L/cow/d (10,800 L/cow/yr), a pregnancy rate of 15% and a milk price of €0.31/L. Three different scenarios where simulated for each one of the dairy herds: (1) CON (without any HS effects), (2) HS (with the HS effects) and (3) HS+CS (with the HS and CS effects). The initial investment in CS (fans and sprinkles) was calculated from average local prices (€65/cow) with a pay-off time of 7 years and operating cost of €6/cow month of operational time. The temperature-humidity index load calculated above ≥68 units was 12,672, 8,633 and 2,228 U/yr for SO, CT and NO, respectively, which are 2,265, 1,700 and 668 h/yr. Estimated milk production loss was of 852, 651, and 210 L/cow/yr and increase in open days of 27, 18 and 5 d for SO, CT and NO respectively. The effects of HS reduce the herd income in −€125, −€56 and −€16/cow/yr for SO, CT and NO, respectively compared with the CON scenario (average gain of €269/cow/yr). The investment in CS improved income in the SO and CT (+€46 and +€27/cow/yr), but reduced the income in the NO (−€5/cow/yr) compared with the HS scenario. In conclusion, results suggest that the profitability of the investment in fans and sprinkles depends on total heat load, being profitable in southern and central but not in northern of Spain.