Gas Fitter Practice Test

As the outlet temperature decreases from a water heater to the heating loop, what happens to the heating output from the air handler?

1. Heating output from the air handler decreases

2. Heating output from the air handler increases

3. Rate of heat transfer from the water to air increases

4. Greater temperature drop through the heating loop

The correct answer is: Heating output from the air handler decreases

As the outlet temperature decreases from a water heater to the heating loop, the heating output from the air handler decreases because the temperature differential crucial for efficient heat transfer becomes smaller. When a heat exchanger, such as the one in an air handler, operates, it relies on a significant difference in temperature between the fluid (in this case, the water heated by the water heater) and the air passing over the heat exchange surface. If the water's outlet temperature is lower, the air handler's ability to transfer heat to the air circulates through it is reduced. Essentially, the less hot the water is, the lower the amount of heat it can transmit into the air, leading to diminished heating output. This is a fundamental principle in thermodynamics related to heat transfer efficiency, where the effectiveness of a heat exchanger is heavily dependent on the temperature gradients maintained throughout the system.