The claims that the electric space heater companies put out about the electric space heater saving you money is just a sales gimmick.
Electric space heaters consume at max wattage 1500 watts per hour. And electric space heater running for 18 hours per day at 8 cents per kwh would cost $2.16 per day or $64.00 per month before taxes.
You might save money on your gas bill but the electric bill will cost you another $64.00 per month and the electric space heater alone will not warm a home or a room very good especially in really cold temperatures.
It would be much more cost effective to turn up your furnace thermostat and just keep the whole house warm.
You have to think of your water pipes in your kitchen and bathroom and anywhere else as well.
If those areas get below freezing you risk frozen and ruptured pipes which can cost a lot to fix and cause a lot of damage to your home which could be costly to fix.
Not to mention electric space heaters can be unsafe as well and are fire hazards if not used correctly.
I use an electric space heater to boost the temperature for a bit but I don't use them to try and save money.
If used to much the electric space heater can cost you a lot of money.