Abstract: An elongated inflatable tubular housing is provided including front and rear wall portions. The front wall portion is constructed of solar radiation transparent material and a panel of solar radiation absorbing material is mounted in the housing and extends between opposite sides thereof dividing the interior of the housing into front and rear compartments between the panel and the front and rear walls, respectively. Air inlet structure is operative to introduce air to be heated into the front compartment at one end of the housing, air pass structure is provided and operative to pass air from the front compartment into the rear compartment at the other end of the housing and air outlet structure is provided and operative to exhaust heated air from the rear compartment. The air inlet structure and air outlet structure include structures for conveying air from the interior of an enclosure to be heated into the front chamber and from the rear chamber back into the enclosure to be heated.