How can I make my ventless gas log set more efficient?

I have a 36000 BTU ventless gas log set installed in my masonry fireplace. The house is a 1300 sqft colonial, and when the fireplace is on it does a decent job of keeping the first floor warm, but as it gets colder I rely more on the furnace. It gets really warm on top of the mantal, so I use a fan there to move the warm air around the house. Since it costs much less to run the fireplace than it does the furnace, is there anything I can do to enhance the heat coming from the fireplace.