Rinnai HDC1600i Latent Heat Exchanger - The Game Changer Your Water Heater Needs The Rinnai HDC1600i Latent Heat Exchanger - it's a genuine deal for anyone who wants to get the most out of their Rinnai HDC1600i continuous flow water heater. Otherwise known as the secondary or recuperator heat exchanger, this high-efficiency heat exchanger does what it says on the tin - grabs hold of the heat from combustion gases that would otherwise just get wasted and puts it to good use - it's a bit of a no-brainer, really, boosting overall system efficiency and saving you big time on energy bills in the process. It's a part that's been designed to Rinnai's own high standards, so you know it's going to fit and perform just like it should. What it does is capture the latent heat from exhaust gases and use it to get the water-heating process back on track - and that