Which material might a high-efficiency furnace's secondary heat exchanger be made from?

A high-efficiency furnace's secondary heat exchanger is often made from stainless steel due to its excellent properties for handling higher temperatures and corrosive environments. Stainless steel is resistant to rust and corrosion, which is particularly important given that the secondary heat exchanger deals with flue gases and condensate that may contain acidic byproducts from combustion. This material's durability contributes to the longevity and efficiency of the heat exchanger.

While copper is also used in some heating applications for its excellent thermal conductivity, it can be more susceptible to corrosion, especially in the presence of acidic condensate. Plastic is not typically used for heat exchangers in high-efficiency systems because it cannot withstand the high temperatures and pressures involved in these processes. Iron, while strong, is prone to rust and corrosion, making it unsuitable for the same reasons as copper, particularly in an environment where moisture is present. Hence, stainless steel is the preferred choice for ensuring durability, efficiency, and performance in high-efficiency furnace secondary heat exchangers.