Fans don’t cool rooms. They circulate air and make people feel cooler, but fans don’t affect the actual air temperature. Running a fan in an unoccupied room wastes electricity.
You might assume that running space heaters in rooms you use regularly would be cheaper than heating your whole house, but it can cost more. Your furnace is more efficient than space heaters.
Leaving electronic devices on all the time wastes electricity. It used to take a lot of energy to power up a computer, but devices have become more efficient.
Electronic devices and appliances can continue to use electricity when they’re turned off. To avoid wasting electricity, unplug devices and appliances you’re not using.
Sometimes utility companies charge different rates at different times of day, but many charge the same rate all the time. If you’re billed one flat rate, then running appliances at night won’t save you money.