NATE Air Conditioning and Heat Pumps Practice Exam

To determine the airflow volume for the residential electric furnace, you need to first calculate the heat output of the furnace in BTUs. This can be done using the formula:

\[ \text{BTUs} = \text{Voltage} \times \text{Current} \times 1.732 \]

In this case, the voltage is 240 V and the current draw is 40 A:

\[ \text{BTUs} = 240 \, \text{V} \times 40 \, \text{A} \times 1.732 \approx 16,638 \, \text{BTUs} \]

Next, with the entering air temperature and the leaving air temperature, we can find the temperature rise:

\[ \text{Temperature Rise} = \text{Leaving Temperature} - \text{Entering Temperature} = 105°F - 70°F = 35°F \]

After obtaining the BTU output and the temperature rise, the airflow volume can be calculated using the formula:

\[ \text{CFM} = \frac{\text{BTUs}}{1.08 \times \text{Temperature Rise}} \]

Plugging in the values:

\[ \text{CFM}