[crazyhorse691]

It is a wonderful idea to redirect that weak acid back into the boiler instead of just letting it go up the stack...especially if you make a living repairing or manufacturing boilers. Overall, not so good for the pocketbook or the environment. The stack is the only winner in this(prolonged life because less acid condense).

[mamelukesabre]

Condensing boilers are stainless so there’s no problem with the products of combustion condensing in the boiler, and condensing boilers don’t use a stack or a chimney. They use PVC out the side of the house just like high efficiency furnaces do.