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There’s nothing wrong with the condensing boiler concept. This is just one particular model with a poorly designed condensation drain. About every 2 to 3 years they need a thorough cleaning, however. That’s more often than the non condensing boilers need. Other than that, there’s nothing to gripe about. On a small house, you may not save enough to make up for the more frequent servicing plus the extra installation costs. But over 2000 square feet house in american upper midwest and new england winters the savings is plenty to justify it.

I can tell that you know something about the subject. I just did a little reading about the condensing boiler and I am puzzled by something the author of this article says:

The condensing boilers were designed to recycle the CO2 emissions and steam that would normally be vented outside and then feed it back into the system through the waste water pipe. The new system was touted to increase efficiency by as much as 93%.

First of all, I believe the author should have said that it will increase the efficiency to 93%, not by 93%. The traditional non-condensing boiler probably operates around 75% efficiency, based on HHV of the fuel.

But my question is not about the efficiency increase. Rather, it concerns the CO2. From what the author says, the CO2 leaves in the waste water, and that is recycled back into the system. For one thing, although some of the CO2 would dissolve in the water, I believe that a considerable portion of it would end up in the flue gas. There is no way to eliminate the flue gas entirely, since most of it is nitrogen which entered with the combustion air. So, implying that all of the CO2 is removed by condensing the water in the flue gas seems deceptive to me.

Additionally, I feel certain that the acidic water condensed from the flue gas would not be recycled into the system. You certainly wouldn't want the dissolved CO2 and H2S going into your boiler. Rather, the wastewater must be dumped somewhere. And neutralized, if your disposal pipe is not made of a material which can tolerate the low pH of the water. Is this not correct?

Now, for the global warming bunch, who justify these boilers partly by this claim of CO2 removal:

1) As I stated above, I don't think it is possible to remove all of the CO2 by condensing the water in the flue gas.

2) Any CO2 which is dissolved in the condensed water in the flue gas, if it doesn't react with an alkaline chemical to form carbonates, will eventually end up in the oceans or the atmosphere. So, it's sort of like sweeping it (the CO2) under a rug and pretending you've eliminated it, when in fact, it comes back to us from another direction.

Do you agree with these points, or am I missing something? Again, I don't doubt the improved efficiency, but this CO2 removal business just sticks in my craw.