Gas Fitter Practice Test

What effect does a dirty cooling coil have on a furnace?

1. The return air temperature will rise

2. The return airflow will increase

3. The bonnet temperature will decrease

4. The supply airflow will decrease

The correct answer is: The supply airflow will decrease

A dirty cooling coil can significantly impact the performance of a furnace, particularly in how it affects airflow. When the coil is dirty, it can obstruct the air passage, making it difficult for air to flow freely through the system. This restriction leads to a reduction in supply airflow, meaning that less heated air is distributed into the living space. In systems where proper airflow is critical for heating efficiency, such as forced-air furnaces, a decrease in airflow can lead to insufficient heating and overall discomfort in the environment. Additionally, the lack of airflow can cause the furnace to work harder to maintain the desired temperature, potentially leading to premature wear on the system and higher energy costs. The other effects associated with a dirty coil, like changes to return airflow or temperature, may occur, but the primary consequence is the decrease in supply airflow, which directly affects the furnace's ability to distribute heat effectively.