PROBLEM TO BE SOLVED: To provide a warm air heater for protected horticulture which is enhanced in heat transfer performance and thermal efficiency by devising a furnace body.SOLUTION: The warm air heater for protected horticulture includes: a casing 101； a cylindrical furnace 110 disposed sideways in the casing, to one end of which a nozzle part 121 of a burner 120 faces, and also at the other end of which a reversal part 112 reversing combustion gas G along the wall surface in the furnace is formed； a first smoke chamber 130 upward leading the reversed combustion gas to the outside of the furnace from a position rather closer to one end of the furnace in the casing； a first smoke tube block 140 guiding the combustion gas toward the other end side of the furnace from the first smoke chamber； blowers 150 attached to the top surface of the casing to exchange heat to the combustion gas via air blasting； a second smoke chamber 160 collecting the combustion gas flowing through the first smoke tube block in the casing； a second smoke tube block 170 guiding the combustion gas downward at a position rather closer to the other end of the furnace from the second smoke chamber in the casing； a third smoke chamber 180 collecting the combustion gas flowing through the second smoke tube block in the casing； and a chimney 190 exhausting the combustion gas from the third smoke chamber to the outside of the casing.
