Minimum hearth dimensions of fireplace.

VF24TDF Model Gas Log Minimum Clearance Requirements

Careful selection of a gas log appliance must include attention to the clearances that are available in your specific installation. Review these minimum requirements as listed in the installation instructions provided with these gas logs.

Minimum mantel height requirement for indicated projection. Note heat resistant material ( not wood )
Minimum  required clearance to any combustible item is 36 ".