The contribution of dry flue gas is ~9-12% & ~5-8% due to presence of humidity & water in combustion products. The reason is that the flue gas temperature (generally 170 - 200°C) is limited by dew point to avoid condensation of downstream exchangers.
In the CHX™ condensing heat exchanger, all gas wetted surfaces are covered with DuPont Teflon~. The Teflon covered heat exchanger surfaces are impervious to all acids normally resulting from the combustion of fossil fuels. This allows the flue gas to be cooled to below the water vapor dew point with no subsequent corrosion of the heat exchanger surfaces. If this heat is not recovered it will account for a boiler's second largest thermodynamic loss.
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