The condensing water heater is a system of technologies, consisting of the water heater itself fuelled by gas or oil, the flue stack, and the condensate collection system. Condensing water heaters operate at around 95% gross efficiency, compared with 80-85% gross efficiency for conventional water heaters.
They achieve higher efficiencies by using newer technology and by condensing the water vapour that is produced during combustion and trapped in the flue gases.
In traditional water heater technologies, the latent heat contained in the water vapour is allowed to escape through the flue. Condensing water heaters reclaim that latent heat by condensing the water vapour and transferring its heat to the return water via a secondary heat exchanger with a resultant increase in water heating efficiency.
