Solar energy fluid heating system

In a hot water system of the type comprising collecting means for heating fluid with solar energy, storage means including a storage tank for storing fluid heated by said collecting means, first fluid conducting means connected between said collecting means and said storage means for conducting fluid from said collecting means to said storage means, second fluid conducting means for conducting fluid to said collecting means, and pump means for transferring fluid through said second fluid conducting means, collecting means, first fluid conducting means, and said storage means, the improvement comprising:

• container means including a predetermined volume of said tank for containing a predetermined volume of air and coupled to said first fluid conducting means, and means including a plurality of taps in said tank located at various heights of said tank for drawing fluid from said tank from any one of said taps so as to adjust the predetermined volume,
• wherein said pump means is operable in an operative mode so that fluid is transferred through said second fluid conducting means, collecting means and said first fluid conducting means to said storage means forcing air into said container means, and a nonoperative mode so that the fluid disposed in those portions of said system exposable to temperatures below the freezing temperature of said fluid is displaced with air from said container means, and wherein said predetermined volume is greater than the volume of said portions exposable to temperatures below said freezing temperatures, and said pump means allows back seepage of fluid when in said nonoperative mode.