Question: We are thinking about converting our pre-fab fireplace over to ventless gas logs. We also tried to get some glass doors but were told we couldn't use them on a pre-fab fireplace. Is this true? Answer: You can use glass doors- but they must be the ones made by the manufacturer of your fireplace to fit that specific fireplace model..there should be a tag on the fireplace stating the make. If you are getting Ventless logs- no need for the glass door. In fact, the glass doors would have to be kept open or removed with Vent Free Logs.<p> Some pre-fab fireplaces are not rated or listed to accept the high heat output of vent free logs. Be sure to check with the manufacturer of your unit.