cast iron or aluminum].” A heat exchanger isn’t necessary in an electric furnace, which doesn’t burn anything. But every gas- and oil-burning furnace must have one. John Gabrielli ...

This is because the channels within a high-efficiency heat exchanger are much smaller than those inside a cast iron boiler and are more likely to clog when decades’ worth of sludge is introduced.

The thermal mass of a cast-iron boiler heat exchanger weighing 400 pounds and containing 10 gallons of water is 14 times greater than that of a 5-pound stainless steel heat exchanger holding 1 gallon ...

Unlike cast iron boilers, circulators on condensing boilers should pump into the heat exchanger to decrease chances of cavitation or steam flashing. Because such boilers may contain only 1/2-gal. of ...