Solar collectors are considered one of the most advanced methods for heating water or air. Their efficiency increases when the solar collectors are directed toward the sun. based on the directional movement of the sun, there must be a sun tracking system, but this system is very expensive, especially in practical applications. In the current study, tests were conducted on the parabolic trough concentrators with different tilt angles (100, 200, 300, 400, 500), which is the angle at which solar rays fall on the solar collector perpendicularly, to reach the optimal tilt angle. It was found that the north-south direction The solar concentrators are better than the east-west direction. The best heating performance of the solar collectors is at a tilt angle of 300. It is also noted that when the tilt angle exceeds 300, the percentage of solar radiation falling on the concentrators is lowered. the tilt angle of 300 is the optimal angle for solar collectors, as it achieved the highest average temperature of the water leaving of the solar collector by 18%.