Are Air Preheaters Heat Exchangers?

Heat Exchangers

• A heat exchanger functions as one of the components within a furnace heating system. With forced-air heating systems, the heat exchanger appears as a metal compartment that sits over top the furnace burners. A home’s return-air duct sends cool air to the furnace unit. The outside walls of a heat exchanger convert this cool air into warm air. As burner combustion processes also generate toxic gases and byproducts, the exchanger sends unwanted gases up through an attached chimney flue and into the outside air.

Air Pre-Heaters

• Air preheaters are commonly found on large-scale water boiler systems, though ongoing technological developments look to adapt air pre heaters to smaller-scale systems. These devices attach to the flue exhaust portion of a heating system. An air preheater appears as a cylinder- or rotor-device containing elements, or heat-transfer surfaces that absorb and transfer heat. As combustion gases from the heat exchanger move upwards, an air preheater absorbs the heat contained in these gases before they go up the flue. An air preheater device uses different sectors within its rotor to allow gases to flow through.

Heat Transfer Cycles

• Heat transfer cycles within an air preheater work to absorb and redirect wasted heat from exhaust fumes discharged by the heat exchanger unit. In effect, air preheaters supplement the heat-generating activities carried out by a heat exchanger. Any heat absorbed by the device gets directed into a home or building’s heat duct system. Air preheaters also include a sealing system designed to prevent air leakage. As heat and gases pass through an air preheater’s casing, the sealing system prevents leaks on both sides of the rotor unit.

Effects

• The use of an air preheater within a heating system helps to increase a system’s heat output and energy efficiency. According to the Natural Gas Boiler Burner Consortium, air preheaters increase boiler efficiency by 1 percent for every 40 degrees of heat generated. Improvements in energy efficiency result from the increase in heat output within the home or building. Increased heat output reduces the length of time a boiler unit needs to operate in order to raise temperatures to the desired level.