When the North American “radiant renaissance” took root in the late 1980’s, nearly all of the boilers used in hydronic systems were “conventional” boilers. That designation means that those boilers are not intended to operate at conditions that would cause sustained flue gas condensation. Examples of conventional boilers include those with cast-iron, steel or copper water tube heat exchangers.
For boilers operating on natural gas or propane, flue gas condensation begins at inlet water temperatures below about 130 ºF. Boilers operating on low sulfur #2 fuel oil have lower dewpoint temperatures in the range of 110 ºF.
