A Noritz water heater cannot be used as a pool heater due to the chemicals that can be harmful to the copper components within the unit. Although a pool heater might be necessary in order to heat up the pool quickly, a secondary heat exchanger specifically for pool applications (made of Titanium, Stainless Steel or Cupro-Nickel) can be used with a Noritz unit to gradually raise the temperature of the pool water.
The hot water from the water heater will indirectly heat the ambient pool water while they are both flowing through the heat exchanger through the connections provided. More information can be found at http://www.heatexchangersonline.com/poolheaters.htm regarding specific models and capabilities.
A device used to transfer thermal energy between two or more fluids (e.g. air, water, oil). The fluids are typically separated and not allowed to mix.