Things in a household that use the most electricity are electric dryers, electric water heaters, 1500 watt electric space heaters, electric ovens, electric fireplaces, furnace blower motors and central A/C or an electric furnace.
Out of all those the central A/C or even the electric furnace would be huge users of electricity.
Central A/C's can use up to 3,500 watts of electricity per hour and an electric furnace depending on size can use up to 18,000 watts of electricity per hour when the heating elements are on.
If the electric furnace runs for 15 hours total per day you can use as much as 270,000 watts of electricity which would cost you around $27.00 per day or $810.00 per month which is a lot of money for barely warm heat.
Natural gas is a much cheaper option for heating your home and you'll be warmer as a result.