Some professionals believe that the condensate produced on the combustion side of the heat exchanger may corrode an aluminium heat exchanger and shorten boiler life. Statistical evidence is not yet available since condensing boilers with aluminium heat exchangers have not been in use long enough.
Some professionals believe that condensate from the combustion side of a heat exchanger may corrode an aluminum heat exchanger and shorten the life of the boiler.  The lack of statistical evidence is due to the recent introduction of condensing boilers with aluminum heat exchangers.