What is likely the outcome of using an oversized mid-efficiency furnace?

The use of an oversized mid-efficiency furnace typically leads to a scenario where the furnace can heat a space too quickly, resulting in short cycling. This means that the furnace doesn't run for a sufficient amount of time to properly distribute the heat throughout the space, which can lead to a low temperature split.

In heating systems, the temperature split refers to the difference between the temperature of the air entering the furnace and the temperature of the air leaving it. An oversized furnace may heat the air too quickly, causing the temperature difference between the supply air and return air to be less than optimal. This situation diminishes efficiency and comfort, as it fails to maintain a consistent temperature in the living space.

While it might be tempting to focus on energy consumption or maintenance frequency, those aspects are indirect consequences of poor sizing. The immediate and direct result of oversizing is the low temperature split, leading to inefficiencies in the heating cycle.