A closed loop fluid thermosiphon that uses solar energy to progressively boost the air temperature passing through it and comprises a heat sink segment capable of absorbing energy from the sun and a heat exchange segment that transfers energy to the air passing through the heat exchange and progressively boosts the air's temperature that is capable of being either used independently with other passive solar elements, as part of a solar energy system, or in combination with active solar elements, as part of a hybrid solar energy system.