What is a likely result of using an oversized mid-efficiency furnace?

The most likely result of using an oversized mid-efficiency furnace is short cycling of operation. An oversized furnace produces heat more quickly than necessary to maintain the desired temperature in the space. As a result, the furnace will frequently turn on and off, which is known as short cycling. This not only leads to inefficient heating, as the furnace doesn’t run long enough to adequately heat the space but can also cause wear and tear on the system, reducing its lifespan.

Additionally, short cycling can negatively affect indoor air quality and comfort, as it doesn't allow the furnace enough time to distribute heat evenly throughout the area. In a properly-sized system, the furnace would run for longer periods, balancing energy use and comfort more effectively. While the other outcomes can also occur in specific circumstances (such as corrosion if there's moisture accumulation or higher noise levels due to frequent starts), short cycling is the most direct and consistent result of an oversized unit.