A spa heats or cools air in the air space surrounding the water containment vessel to heat or cool the water in the water containment vessel. The air is heated and cooled and is circulated within the spa cabinet in contact with the underside of the tub and the plumbing for transferring or absorbing heat from the water through the tub and the plumbing. The air is heated by a solid state thermoelectric device or a conventional space heater and is cooled using a solid state thermoelectric device. Preferably a single thermoelectric device is mounted through a wall in the spa cabinet and is used for both heating and cooling the air in the air space.