Hayward Universal HC Series HDF400 Dual Fuel Heater allows replacement of almost any heater in an existing pad with the efficient reliability of the new Universal HC Series dual-fuel technology heater from Hayward®. Built to fit effortlessly with Hayward plumbing adapters, every detail has been thoughtfully engineered with easy drop-in capability in mind—its dual-fuel technology, its adaptive plumbing, its zero wall-clearance design, and more. And it all adds up to a durable, ultra-powerful heater with the industry’s smallest footprint.