| http://www.w3.org/ns/prov#value | - Heat pump water heaters can be purchased as integral units with built in water storage tanks or as add-ons that can be retrofitted to an existing water heater tank.Because of the amount of wiring involved, the work is best done while a house is under construction and the walls are open - retrofitting this much cable, unless you do not object to exposed conduit, can add considerably to the cost.Ther
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