The High Performance Series water heaters can provide 155 gallons from the 25-gallon model (GX2-25S) and 200 gallons from the 55-gallon model (GX1-55S) when tested to the industry standard residential First Hour Delivery procedure. The Series combines four design technologies, including inputs of 78,000 BTU/hr for the GX2-25S and 80,000 BTU/hr for the GX1-55S. The helical fin flue design helps to achieve thermal efficiency ratings of 82%. The Optimizer Temperature Control System allows water in the tank to be stored at higher temperatures (up to 180°F) while controlling the hot water outlet temperature to a safe level.