Here is a shot of a 1/2" copper pipe in use to carry the condensate away on a high efficiency furnace. Note the severe corrosion that occured over a 10 year period.The copper pipe as been totally corroded away. The pH of the condesate was measured at 2.5! For this reason Toronto installations must have 1. PVC or CPVC pipe and 2. a pH neutralizer installed. The acidic condensate will ruin mortar joints in old clay sewer pipes and play havoc with the sewage treatment plant.