Before purchasing gas logs please understand that there are two types of gas logs, just as there are two types of gas. Vented Gas Logs are rated as a "Decorative Gas Appliance". Meaning they look pretty burning but don't prvivde a significant amount of heat, since they MUST be operated with the Fireplace Damper fully open.
Vent-free or Ventless Gas Logs are rated as a Supplemental Gas Heating Appliance. But once size does not fit all.  In addition to the correct physical size to fit your fireplace, the BTU output must be calculated correctly.  In which case more is not better, as Vent-free Gas Log Sets are 99.9% efficient.  Also, installation is not a DIY project.  It should be installed by a certified gas technician or your Home Owner's Insurance may not cover you for a loss.  Equally important, be sure to buy the right gas type, Natural Gas or LPG (Liquid Propane).  Vent-free/Ventless CAN NOT be converted from one gas type to another.  And finally, never ever try to install a blower with a Vented Gas Log Set in a solid fuel burning fireplace (ie, masonry fireplace).  It will not increase the efficency, it will only blow soot throughout your house.

Vent-free Gas Log Sets are great supplemental gas heating appiliances.  But, common sence should prevail when making a purchase.  Buy from a reputable dealer who will not only assist in making the right purchase, they can also install it for you.