Abstract: A high-efficiency portable spa is provided for therapeutic and recreational use which includes a tub, a flow generator for circulating water in the tub, and a two-section insulating cover. A heat generator is located adjacent an outlet of the flow generator uses a constriction member in a fluid passageway to frictionally generate heat from the passage of fluid therein and also to reintroduce water circulating through a heat scavenging coil surrounding the flow generator. The tube is advantageously provided with a shell, a frame for supporting the shell, a flexible web barrier surrounding the frame, a skirt surrounding the web, and insulating foam which adheres to the web barrier so that, during curing, the skirt is isolated from shrinkage, crinkling or warping. The cover is provided in two sections and hinged therebetween. The edge of the cover rests on the shell of the tub, and one of the sections may be folded out of the way to provide access to the tub while substantially insulating the remainder.