The solar hot and solar cold pipes between the solar storage tank and the solar collectors shall:
be of DN15 bendable grade or hard drawn copper tube.
Annealed or soft copper shall not be used.
have a continuous fall from the solar collectors to the solar storage tank of a minimum 5° (1 in 10 grade)
and be of a design to ensure complete drain back of the closed circuit fluid.
Care must be taken to ensure the pipe work maintains a continuous fall over the life of the installation.
Pipe work should be fixed at regular intervals to assist in maintaining this requirement.
not exceed the maximum recommended lengths as specified in the table.
Maximum recommended total combined pipe length (solar hot + solar cold)
and number of 90° bends
Pipe Size
1 or 2 Collectors
3 Collectors
Pipe Length
90° Bends
Pipe Length
90° Bends
40 metres
30 metres
For each additional 90° bend, reduce the maximum total pipe length by 0.5 metres.
For each additional metre of pipe length, reduce the number of 90° bends by two.
Note: One 90° elbow is equal to two 90° bends.
It is important to connect the solar hot and solar cold pipes to the correct connections at the solar collector
and at the solar storage tank.
The solar cold pipe connects to the bottom of the solar collector array and may connect to either the left
or right hand side. The solar hot pipe must connect to the top of the solar collector array diagonally
opposite to the solar cold pipe connection. The solar hot outlet connection is to be the highest point of the
The lowest corner of the solar collector installation in a closed circuit system, which is where the solar cold
pipe connects to the collector array, should be the corner closest to the solar storage tank. This will
maximise the gradient for the continuous fall of the solar cold pipe, by providing a shorter lateral distance
for the vertical fall of pipe work.
The hot sensor connection is at the top of the solar collector array, directly above the solar cold inlet
connection for this closed circuit system.
Refer to “Warning: Plumber – Be Aware” on page 29.
It is essential for these requirements to be followed for the system to operate correctly and efficiently. Solar
pipe work which is oversized, or does not have the correct fall, or is too long can result in the drain back system
not operating effectively.
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