Red Circle Solar – Solar hot water products & Closed Coupled Evacuated Tube Solar Hot Water

Solar hot water is a complex subject and before deciding on which system suits your application best, please call or email us to discuss in detail.

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Close coupled/heat exchange systems

250ltr on roof evacuated tube solar hot water.



  • For Domestic  and commercial applications.

Red circle solar offer a range of close coupled evacuated tube solar hot water solutions to suit any situation. Tank sizes for the on roof systems are 165ltr with 20 tubes, 200ltr with 24 tubes and 250ltr with 30 tubes. For larger requirements the tanks can also be connected together in a manifold.

  • Low pressure stainless tank with a high pressure heat exchange coil.

The water in the storage tank is separate to the water used at the tap. When hot water is needed, cold waterenters the submerged 30 mtr x 14mm-copper heat exchange coil, which runs down the centre of the tank, extracts the heat from the stored water instantly, and exits the tank hot. Having a low-pressure tank means that the system can be connected to a wood fire booster and elevates the issue of a PTR valve dumping heat from the tank once it reaches 100Deg C. The excess energy is vented to atmosphere via a open 3/4'' fitting.  

  • "Wet tubes" use the sun's energy to directly heat the water in the tubes.

The tubes are full of water and sealed to the storage tank using a triple silicon O-ring. The sun heats the water in the tubes directly then thermosyphons into the storage tank. No need for pumps or controllers. 

Evacuated tube information.

  • Ideal for Wet backs/Wood Heaters.

To connect a wood fire boosted solar hot water with a wet back or any wood boiler, the tank must be open to atmosphere. A fire is an unregulated heat source and cannot be under pressure. The close coupled system have flow and return ports built into the tank so a wood fire can be directly connected without the use of an external heat exchanger. 

  • Eliminates unnecessary boosting.

Please refer to our article on this by clicking HERE

  • Great flexibility for boosting options.  

Wood fire boosted.

Electric element boosted. 2.4KW

Gas instantaneous boosted. 65 deg or 50 deg booster can be used. 

Pre heat system to either an existing electric or gas storage system.

  • Best suited to metal roofs. 

 The close coupled evacuated tube  systems come with either a 15 deg pitching frame for pitched roofs,  or a 40 deg pitching frame for flat roofs. A tile roof can be suitable but extra care is needed in mounting the frame as the weight on the roof can crack the tiles. We do stock metal top hat battens and also special long threaded bolts to mount to tile roofs. Please ask for more details.

  • Suitable for high frost areas

The evacuated tubes are frost resistant to Negative 30 Deg C. 

  • 10 year manufacturers warranty on tanks frames and tubes.


30mtr x 14mm copper heat exchange coil used in close coupled evacuated tube systems.


How it works

  • Heat exchanger.

The close coupled evacuated tube system uses a 30 mtr 14mm copper coil to transfer the heat from the low pressure storage tank to the mains pressure water used in the house. As the water enters the tank through the mains water supply line, it passes through the heat exchanger and extracts the heat instantly. 


Low pressure tank technical drawings.


  • Low pressure storage.

Having a low pressure storage tank with high pressure heat exchange has many benefits. 

No legionella risk.

Open vented to safely relieve the pressure from the water expanding due to heat.

Wood fire boosting ready.

Low manufacturing costs.


Red Circle Solar uses 1800 x 58mm high quality evacuated tubes with tri coating technology.  Our split system manifolds use the same evacuated tubes combined with a heat pipe. Wet tubes are directly heated by the sun and transfer the heat to the water that is in the storage tank using a thermosyphon

  • Mounting frames.

The on roof system comes with either a low (15 deg)  or a High (40 deg) pitching frame.  The low frame is designed for existing pitched roofs and the high frame is designed for flat roofs or ground mounting. 

Low frame building guide

High frame building guide

  • Solar powered tank filling kit.

The low pressure storage tank is kept full using a 12 volt solar powered solenoid coupled with a stainless steel Reed switch float. If the tank water level drops due to evaporation, the float opens the solenoid and lets water enter the tank. Once the tank is full again, the float rises and shuts the solenoid, turning off the water. All powered by the sun!

More info

  • Boosting.

Every solar hot water system needs boosting in the winter as the days are shorter and the solar radiation is less due to the sunlight passing through  more atmosphere. 

The close coupled heat exchange tank can be boosted using any of the following: