The most significant sources of heat include conventional stoves and ovens, clothes dryers, dishwashers, water heaters, conventional incandescent lights, aquarium lights and heaters, television sets, and computers. In the summer internal heat sources become a liability.

Heat Source: Incandescent lights
Contribution to Internal Heat Gain: Major
Cheap Option: Use lights more sparingly. Turn lights off when not in use.
More Costly Option: Replace with compact fluorescents. Install occupancy sensors.

Heat Source: Water heater
Contribution to Internal Heat Gain: Major
Cheap Option: Turn temperature down to 120F. Install insulation: water heater blanket. Insulate hot water pipes.
More Costly Option: Replace old models with on-demand (tankless) water heaters.