Drain Back Solar Water Heating System 


Drain Back Systems are suitable for single and multiple applications. They are suitable for areas with questionable water quality and moderate climate conditions. They are particularly suitable for single application pools and spas. Domestic hot water and multiple application systems require heat exchangers. These can be small vented reservoirs with separate heat exchangers, or preheat tanks with single or multiple integral heat exchangers. Heat can be thermosyphoned from the reservoir or it can be pumped using a second pump. Single application pool and spa systems can circulate the pool/spa water directly through the collector, using the existing circulating pump and a simple bypass. Reliable freeze protection is provided by the fact that when the pump is switched off, or in the event of a power outage, water in the collector circuit drains back, leaving no water in the collector to freeze.


NOTE: The information presented in this page is for guidance only - no part of this may be used for any agreement, whether express or implied, or to form any contract. THERMO TECHNOLOGIES reserves the right to change specifications and prices without prior notice.


A drain back system requires a large pump. It must have sufficient capacity to lift the fluid to the highest point in the system. When there is no more heat to be collected, the controller turns the pump off, and all the fluid drains back to the reservoir tank. The collectors are empty. They can't freeze, and they can't overheat the antifreeze. As a Do It Yourself homeowner, you won't need a special charging pump either. When it comes time to change the antifreeze, you can just drain and refill the reservoir tank.

  • A circulating pump operated by a differential control is turned on when the collector outlet is at least 20°F (11°C) warmer than the tank outlet.
  • Water or an antifreeze solution is lifted from a small reservoir tank and circulated through the collectors and back to the tank.
  • Heat is transferred to the domestic water via a heat exchanger in the reservoir tank. The circulation loop through the collectors is a closed loop. The water or antifreeze solution is installed at the time of installation, and does not present a recurring supply of oxygen.

  • They allow excellent freeze protection, even in a power outage.
  • The closed loop protects the system from the effects of hard water.
  •  Multiple applications are possible from the same collector. In the unlikely event of a leak, only the water in the reservoir will be spilled.
  • A heat exchanger is required for most applications which reduces efficiency.
  • A high-head (larger) pump is required.
  • And care must be taken (adequate slope to drain) to plumb the supply and return so that they will drain back.

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