What does "condensing" mean?

A condensing boiler attains very high level of fuel efficiency by keeping its burn rate (fuel usage) as low as possible. One result of that is that there is no excess heat left inside the boiler: it all is transferred to the water being circulated. This means that the ambient temperature is low enough that water vapor in the air can condense on the material. One problem that can arise is that impurities in the water vapor can concentrate in this condensation, leading to corrosion. Ray is engineered so that condensate is actually blown into a corrosion-proof container that removes it from the system.