Improved Combustion System Efficiency

New boilers generally incorporate several new technologies. These same technologies can also be applied when retrofitting older boilers. The most important new technologies are as follows.

* Fan-assisted combustion: Originally, boilers and furnaces relied on natural draft, i.e., the buoyancy of the hot air in the flue, to draw the air into the firebox and up the flue. A draft hood limited condensation in the flue and ensured that the burner and flame were isolated from outside air pressure fluctuations by adding "dilution" air to the flue. At the same time, the dilution air lowered the vapour pressure at which the flue gases would condense and cause damage to the flue. However, efficiency was lost because of the loss of heated interior air up the chimney.

Newer-technology fan-assisted burners eliminate the draft hood and are better at mixing fuel and air. As a result, excess air is reduced. Fan-assisted burners also diminish losses by reducing the amount of hot air going up the chimney.

The fan also improves the heat transfer inside the boiler by improving combustion gas flow through the heat exchanger.

Two types of fan-assisted systems are available: a forced-draft system uses a fan to blow the fuel and air mixture into the boiler; an induced-draft system has the fan located at the outlet end of the heat exchanger passages.

* Motorized dampers: Motorized dampers stop heat from escaping up the chimney by automatically closing the flue when the boiler is idle.

* Electric ignition: Older gas boilers have pilot flames that remain lit whether the boiler is firing or idle. Electric ignitions or other intermittent ignition devices eliminate this waste of fuel. A control circuit energizes the ignitor and, if the burner does not fire on the first try, the ignitor re-fires until the burner is lit.

* Sealed combustion: Sealed combustion controls the combustion process more carefully by preventing boilers from inducing infiltration into the building. In a sealed combustion boiler, air is drawn directly from outside through a sealed venting system, ensuring that heated indoor air is not mixed with the outside air during the combustion process.

* Pulse combustion: Instead of a continuous flame, pulse systems create discrete, rapid combustion pulses in a sealed chamber. This intensely turbulent process results in a highly efficient heat transfer to the heat exchanger and allows for flue gas condensation in condensing boilers.