Our company has done several vented log to vent free log conversions over the years. Vented logs provide that natural wood fire look while loosing most of the heat up the flu. Vent free logs don't look as good however all your heat is radiated out into the house. Great for a backup heat source when the power fails. If you purchase vent free you can seal up the flu with sheet metal. Make sure your chimney cap is still good and you should pay to have it checked out for structural problems that could lead to water damage.
Some safety tips:
1. ALWAYS have a carbon monoxide detector in your home if you have any appliances that us natural gas, propane, fuel oil, kerosene, or even if you burn wood. REPLACE the batteries annually. REPLACE the detector every 10 years.
2. DO NOT use a glass enclosure over vent free logs unless you purchase a fireplace insert that has one. If your fireplace has glass doors and you put in a set of vent free logs make sure you open them when you use them.
3. Everybody wants to save a dollar. Me included, but I would recommend you talk to a local heating and air conditioning contractor for your specific needs. The people in the hardware stores, I. E. Lowes, Home Depot, Menards, Ace Hardware are sales people not installers and or technicians.:faint2: They may be well trained, but our company for example has liability insurance to cover us if we screw something up and mess up your house. Or burn it down!
Just .02 cents from a Nate certified Technician here though.