When should a heat pump go into defrost mode due to ice build-up?

A heat pump should switch to defrost mode when ice build-up exceeds a thickness of 1/8 inch. This is important because as ice accumulates on the outdoor coil, it reduces the heat pump's efficiency by obstructing airflow and impairing heat transfer. When ice thickness exceeds this specific threshold, the heat pump can struggle to maintain its heating capabilities, which can lead to decreased performance and damage over time.

Maintaining operational efficiency is critical, especially in colder weather when heat pumps are most needed. The defrost cycle is designed to allow the heat pump to use its heating function to warm the coil and melt the ice, ensuring that the system continues to operate effectively. Choosing the correct thickness for activating this mode ensures that ice is dealt with promptly, thus maintaining optimal performance and reliability in heating the home.