Abstract: A gas fireplace insert for inserting into existing solid fuel fireplaces is made into modules that are separable for installation and can be later assembled together. A housing module which includes a combustion chamber supports a separable module comprising a duct for fresh air intake. The duct includes a connection collar for an air intake pipe leading to the interior of the duct. The duct also has a pass through collar for carrying exhaust gases from the fireplace. The collars can be attached to an exhaust pipe and air intake pipe respective, which extend through the existing chimney. The duct module is separated from the housing module for installation so that the pipe connections are easier to make with the lighter, smaller module.