Direction of Airflow in a Furnace

Parts of a Furnace

• To understand airflow in a furnace, you need to become familiar with the major parts of a furnace. The blower motor with the blower fan installed on it is found at the base of the furnace, and it moves air into the heating chamber. Within the heating chamber is a sheet of metal in an S-shape that is the heat exchanger. This is where the air is heated and then forced into the home through the duct work. The airflow in your furnace is from the blower fan to the heat exchanger. The heat exchanger is housed inside the large metal box that most people generally refer to as the furnace.

Filter

• The placement of your filter depends on where the blower is located in relationship to the heat exchanger. If the air moves from the bottom of the furnace upward towards the exchanger, this is referred to as an upward-flow furnace. The filter will be located at the bottom of the unit near the blower. If the blower is at the top of the furnace moving the air downward, this is referred to as a down-flow furnace and requires two filters that are installed inside the compartment housing the blower motor.

Efficiency

• Determining proper air flow is important because it allows you to install the filter properly. If the filter is not installed to go with the airflow of your furnace, it will not be able to filter out debris and allergens to protect the people in your home. An incorrectly installed filter also inhibits airflow and reduces your furnace's efficiency.

Maintenance

• A furnace filter should be changed at the start of fall, prior to turning the furnace on to combat the cold weather. During peak usage, a furnace filter should be changed every three months to maintain efficiency.