A natural gas fireplace is a very energy efficient heating appliance and they look nice too.
My natural gas fireplace costs me 19 cents per hour to run and I run it around 8 hours per day which costs me $1.52 per day to run and in 30 days it costs me $45.60 per month before taxes and other charges.
So you're not paying much at all for the natural gas fireplace to run an natural gas is one the cheapest form of heating fuel you can buy.