As the outlet temperature decreases from a water heater to the heating loop in a combination system, the:

As the outlet temperature decreases from a water heater to the heating loop in a combination system, the heating output from the air handler decreases. This relationship is based on the principles of thermodynamics and the efficiency of heat transfer in a heating system.

When the temperature of the water decreases as it travels from the heater to the air handler, it carries less thermal energy. The heating output, which is the ability of the air handler to warm the air being circulated in the space, directly correlates with the temperature of the water entering it. A lower inlet water temperature results in less heat being available to transfer to the air, thereby reducing the overall heating capacity of the air handler.

This impact on heating output is significant because the air handler's effectiveness is primarily determined by the temperature difference between the water entering the unit and the air it is heating. With a decrease in outlet temperature, there is less energy to transfer, leading to diminished heating performance.

Other options reflect misunderstandings about the relationship between temperature and heating output or confusing concepts like the rate of heat transfer or the implications of temperature drop along the loop, which would not result in an increase of heating output in this scenario.