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True, but I'm already wasting heat due to having a tank-based hot water heater. Adding the volume of the water pipes into that is probably not terribly significant.


It's not the volume, it's that you'll be running heated water through several meters of uninsulated piping. This will make a fairly effective radiator.

Typically, in houses built with hot water recirc systems, the hot water loop is well insulated in it's entiety. Still, there will be heat loss one wouldn't get if one didn't recirc the hot water.