In an improved swimming pool water heating system, water in the pool circulates through a first loop from the pool to a surge pit and through a filter before returning to the pool. The heating system includes a second loop with a heat exchanger in the surge pit and a remote water heater. The pool water in the pit is heated by the heat exchanger. The first and second circulation loops are separate from one another. The heater may include multiple heating units which can be staged for sequential actuation, depending upon need. The second circulation loop is closed, such that the pool water does not flow through the heater, but rather is indirectly heated via the heat exchanger. The heater is isolated from the pool water.