The exchanger is where gas heaters and heat pumps differ most in how well they take Florida water.
| Material | How it holds up | Models here |
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| Titanium | Titanium doesn't corrode in pool water, so it's the standard on quality heat pumps and the reason a heat pump can sit on a salt pool for years without exchanger trouble. It costs more, which is why it's rare on gas heaters, and the ETi 400 is the exception here. |
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| NiTek nickel alloy | A nickel-alloy exchanger that Raypak offers on its AVIA HD gas heaters as a corrosion-resistant alternative to copper. It sits between cupro-nickel and titanium in resistance and price. |
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| Cupro-nickel | Copper alloyed with nickel gives up a little heat transfer in exchange for much better resistance to unbalanced water chemistry and salt. On a gas heater this is the upgrade worth having near the coast. |
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| Copper | The traditional material and the cheapest to build. It transfers heat well and does fine on well-balanced chlorine water, but it's the least forgiving of low pH, high chlorine and salt. Water chemistry has to stay in range for a copper exchanger to reach its full life. |
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Where a chlorinator or salt cell is installed, it belongs downstream of the heater. For the full gas, heat pump and solar trade-offs, read heat pump vs gas vs solar, and size the unit with the pool heater size calculator.