Rinnai HDC1600i Heat Exchanger The Rinnai HDC1600i Heat Exchanger is a actual replacement heat exchanger core that is made to be a exact fit for the Rinnai HDC1600i continuous flow water heater. It's essentially the heart of your tankless system thats sole job is to move the energy from the burner to the water, so you get hot water on demand without losing efficiency or reliability. Designed and built to Rinnai's exacting standards, this heat exchanger is the perfect tool for people who want optimal heat transfer, corrosion resistance , and years of long term performance. In fact, swapping out a heat exchanger that's worn out or on it's way out can actually give your water heater a new lease on life, reduce service calls, and help keep your system running strong for years to come. ⚠️ Warning: Replacing or