Energy Star certified with a UEF of 0.95;Easily maintain like-new performance by adding X3 Scale Prevention at any time with an optional X3 cartridge (sold separately) ;Flexibility in Installation—PVC venting flexibility (2” up to 50’ & 3" up to 150’), Install indoor or outdoor (outdoor kit sold separately);Expandable for Larger Applications—Cascade up to 12 like heaters when multiple water heaters are required to work in conjunction (cable included);Built-in Control Display—Check status, error codes and settings