NATE Air Conditioning and Heat Pumps Practice Exam

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Ace your NATE Air Conditioning and Heat Pumps Exam with our quiz. Prepare with detailed questions, hints, and thorough explanations to boost your confidence and guide your study journey. Get ready for success in your HVAC certification!

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What is the indoor air flow for an electric furnace when the supply air temperature is 98°F, the return air temperature is 70°F, the voltage supplied to the furnace is 220 V, and the current draw of the furnace is 47 A?

1,060 CFM
1,170 CFM
1,260 CFM
1,370 CFM

The correct answer is: 1,170 CFM

To determine the indoor air flow for an electric furnace, we can use the formula that relates air flow in cubic feet per minute (CFM) to the heat output of the furnace. The heat output can be calculated using the formula: \[ BTU/hr = Voltage \times Current \times 3.413 \] In this scenario: 1. **Calculate the BTU/hr**: - With a voltage of 220 V and a current draw of 47 A, the equation becomes: - $ BTU/hr = 220 \times 47 \times 3.413 $ - $ BTU/hr = 220 \times 47 \times 3.413 = 33,994.84 \ BTU/hr $ (approximately) 2. **Calculate the temperature difference (TD)**: - The temperature difference between the supply air and return air is: - $ TD = Supply Temperature - Return Temperature = 98°F - 70°F = 28°F $ 3. **Determine CFM**: - Using the heat output and temperature differential, air flow can be figured out as follows: - The formula converts BTU/hr and temperature rise into CFM: