Ground source heat pumps are incredibly efficient, with an output that is three to four times the amount of energy that goes in, which is an efficiency rating between 300–400%. Even the most efficient gas boilers can never go over 100% efficiency.
You also get year-round heating consistency because ground source heat pumps use the ambient temperature of the soil. The warmth in the soil remains constant throughout the year, making ground source heat pumps highly effective in the winter.