I have a wood burning fireplace in my apartment with gas heating. Is there a feasible way to board it up?

I have small children, and I also don't want to incur the cost of getting firewood, not to mention finding somewhere to store the firewood. I really don't want to be bothered with the upkeep since it would probably cost more to use than just running my gas heater this winter. How do you recommend I close it off so that I don't lose any heat?