Room heater advice - does it help in lowering bill

Hi All,

We are just two poeple leaving in a big house of 3000 sq ft. Somebody
told me that if lower the thermostat setting to 65 during the night
and buy a room heater we might save some money in bills?

Is it true? Because we have gas heating and normally putting room
heater for whole night will put up the electricity bill?

Please need your advice?

Thanks and Regards,
Vandana