Keep in mind that many older homes were not wired to accommodate all of the new appliances used today. These may include microwaves, computers, coffee pots, toasters, unit heaters, and air conditioners, just to name a few. You need to take steps to avoid overloading the system.
Many people don't realize that a space heater usually requires its own circuit. Did you know that you can be shocked off the space heater frame? Even worse, if the circuit is over-fused, this can result in an electrical fire.