If a customer complains that the furnace is blowing cold air at the beginning of a heating cycle, what could be the cause?

The reasoning behind identifying that the fan setting may be too low as a cause for a furnace blowing cold air at the beginning of a heating cycle centers on how a furnace operates. In many heating systems, the fan continues to run even when the heating element is not producing heat initially. If the fan speed is set too low, it may not be able to effectively circulate the warmed air once the heating element begins to work. Consequently, this can lead to a perception of cold air blowing from the vents until the heat has more fully distributed.

While the other options also deal with potential issues that can affect furnace operation, they do not directly address this specific symptom. An interrupted fuel supply would typically lead to no heat at all rather than just a delayed response of cold air. A malfunctioning thermostat could cause improper heating cycles or temperature readings, but it does not directly indicate why cold air would be blown at the start of a heating cycle. Similarly, an incorrectly set heat anticipator wouldn't typically result in a temporary blast of cold air, but rather could affect the overall efficiency of the heating cycle. Thus, the low fan speed stands out as the most direct explanation for the observed issue of cold air at the onset of heating.