Space Heaters

Assuming you live in a small apartment, rather than a large house, I'm going to guess that your average yearly power consumption is 700 watts. If that was the case, then here's how it would work out.

Let's say you run the space heater for 1/4 of the year (3 months of winter), and during that time, you run it for 1/12 of the day (2 hours per day) on its highest setting (1500 watts). The amount it adds to your yearly average is:

1/4 * 1/12 * 1500 W = 31.25 W

That brings you to 731.25 W yearly, or a 4.5% increase in power consumption. Thus, your electricity bill would increase by 4.5%.