The above example applies only for an air source heat pump. The above example assumes that the heat pump is an air-source heat pump moving heat from outside to inside, or a water-source heat pump that is simply moving heat from one zone to the other. For a water-source heat pump, this would only occur if the instantaneous heating load on the condenser water system exactly matches the instantaneous cooling load on the condenser water system. This could happen during the shoulder season (spring or fall), but is unlikely in the middle of the heating season. If more heat is being withdrawn by the heat pumps that are in heating mode than is being added by the heat pumps that are in cooling mode, then the boiler (or other heat source) will add heat to the condenser water system. The energy consumption and cost associated with the boiler would need to be factored in to the above comparison. For a water-source system, there is also energy associated with the condenser water pumps that is not factored in to the heat pump energy consumption in the example above.