Hayward Heater, 5.5 kw Electric Spa/Hot Tub ComfortZone: Hayward electric spa heaters contain all of the sophisticated features and capabilities of heaters twice their size. The electric heaters fit into compact spaces - even under spa skirts or steps. Like all Hayward heaters, they are easy to install and service.(Heaters must be installed by a pool professional in order to keep warranty valid.)