The copper is for the heat exchangers that fit against the wood stove, and around the water heater. Better heat transfer with conduction of the copper against the metal. Also for possible over-heat conditions. Just the heating loop is copper and braided stainless flex lines. All the water piping is pex, Pex is piped to the sink, shower, water tank etc, you can see some white and red under the sink. I’m a plumber by trade, so I know pex well. Thanks for the comments
