Marketing InformationMegaTherm Pool Heaters are designed for commercial, institutional and large residential where economical performance and rapid heat-up are required. Available in indoor and outdoor models in both natural and propane. MegaTherm is design verified to the ANSI Z21.56 Standard for Gas-Fired Pool Heaters (Outdoor 5---1825 units are certified for use without the addition of a draft diverter or external vent. Indoor units incorporate a built-in draft diverter and require only vent piping.)