Setback is hard to cut. Also hard to make bend, so advisable to use one piece of copper for end bending and positioning especially to be concealed in the wall.

I mean cutting ss is more difficult to cut copper. ss though is thin but tough. The cutting knife blunted easily after cutting few piece unlike cutting copper. So have to use saw.
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Yes there are socket you can make 90 degree turn but sometimes there are 60 degree turn or 50 degree turn or long turn (not sharp turn) due to obstacle like existing pvc pipe in the way and you need no socket to make these bends.
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Got angle ss ma. Why need to use copper in between.

Let's say the cold pipe out let and hot pipe outlet has to be 6 inches apart but it is a little more than 6 inches (for rain shower installation). You can bend along the copper pipe line to be closer to the pvc cold pipe easily. Of course you can bend pvc cold pipe but you either fire(heat) it then bend to position or use a nail to hold it in position before cement/concrete.

Nice sharing

Installation RM300, 6 foot piping RM600. Total RM900 for this kind of heater simple installation!!!

Do you know that installation for a 60 gallon solar heater is only RM600 which includes

1. Two skilled workers with long ladder dangerously take the heater up the roof. Secured the brackets, install and put the 60 gallon tank in position,
2. fix the non-return valves two pieces,
3. one hot and one cold steel stop valves
3. copper piping one cold to tank and one hot to hot inlet (to bathrooms)
4. Connect heater element to power source at the roof.
5. Pressure testing for leak by switching on pump
6. And if pump bought together with solar heater, pump installation is free of charge

So much work and materials.