I use 1/2” rigid copper pipe in my system. I just wrapped any part that could be a heat loss issue with pipe insulation, to include valves. I re-circulate the water in my e-HLT to speed up the process and keep it from stratifying; it does not appear to have much heat loss. Heat loss through an un-insulated hose, or an un-insulated pipe would not be much difference, at least not with the short distances you’d see in a HB setup.
I do not have a HERMS setup though, and have a constant heat source.
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