Why?
Good question....
In the view of CSA there are serious safety factors involved, that they need to protect the public from.
- One is the collector being blown off the roof.
- Another is when water reaches stagnation and can have a steam rupture.
- and there are more to do with potable water cross contamination.
The CSA Engineer says that without standards, manufacturers and DIY would take the lowest road possible. I agree, but do not like it.
I wish industrious people like us could make a solar collectors from copper pipe and recycled windows, and use a recycled chest freezer for thermal storage, then just drop a roll of PEX connected to the DHW tank. VIOLA - a darn good system for $500, and recycling too! Only in the boonies where inspections are not required.