How Does a Heat Exchanger in a Gas Furnace Work?

Gas furnace heat exchangers are hollow and heated from the inside, allowing dangerous gases to exit the chimney.

Gas furnaces are known for their safety and longevity. However, heat exchanger problems do have the potential for products of combustion to leak into conditioned, occupied space via air ducts.

Construction

Many modern gas furnace heat exchangers are comprised of steel, clamshell-shaped sections called chambers. The number of chambers depends on the heating capacity of your furnace. Each chamber is hollow and includes two openings, one at each end.

Heating Operation

A heat exchanger chamber is heated from the inside through one opening while the second opening draws the products of combustion out of the home's chimney. Once the heat exchanger is heated to the factory temperature, the furnace's indoor blower motor blows air between and over each heat exchanger chamber to warm the house.

Safety

Heat exchangers expand and contract as they are heated and cooled when the furnace cycles. The expansion and contraction can lead to cracks in the steel chamber, potentially releasing dangerous carbon monoxide into the living space.

References

• American Gas Association Heat Exchanger Test
• Heat Exchangers Online
• Bob Vila Video: Installing a New Gas Furnace
• Energy Star: Furnaces and Boilers