Rinnai 16i HEX Intercooler (P16I-KITB2) The intercooler — more properly the secondary heat exchanger — on a Rinnai 16i series water heater recovers heat from the exhaust gases and feeds it back into the water heating process. It's a key part of what makes these condensing units efficient, capturing energy that would otherwise be lost rather than letting it go straight up the flue. This genuine Rinnai intercooler is made to the original specification for the 16i series, restoring reliable heat recovery and helping maintain both efficiency and consistent hot water delivery. Whether the unit is simply getting on in years or a specific component has worn out, fitting a genuine replacement intercooler is a meaningful step in keeping the system performing as designed. ⚠ Important: This part should only be installed by a Gas S