A method for cooling or heating a building is provided. An air flow can be created in an air duct and the air flow can be cooled or heated by an air conditioning system or furnace. The cooled or heated air flow can then pass through a heat exchanger connected to a radiant heating loop running through a floor or slab with a liquid circulating through them. When the airflow is being cooled or heated by the air conditioning system or furnace, the air flow will alter the temperature of the liquid circulating through the heat exchanger herefore the temperature of the slab. When the temperature of the slab varies from the temperature of the building, liquid that has been circulated through the radiant heating loop can be used to alter the temperature of the air flow passing through the heat exchanger.