Which of the following can decrease the efficiency of a heat pump?

Lower levels of insulation can significantly decrease the efficiency of a heat pump because they allow more heat to escape from a conditioned space. When insulation is inadequate, the heat pump has to work harder to maintain the desired indoor temperature. This results in higher energy consumption, as the system runs longer to compensate for the heat loss, leading to increased operational costs and a reduction in overall efficiency.

In contrast, other factors mentioned, such as increasing the ambient temperature, having an optimized heating schedule, and performing regular maintenance checks, generally contribute to improved efficiency or have minimal negative impact. Higher ambient temperatures can help reduce the amount of work the heat pump needs to do, while an optimized schedule can ensure that the system operates only when necessary. Regular maintenance ensures that the heat pump runs smoothly and efficiently, preventing issues that could lead to inefficiency.