How to Improve the Energy Efficiency of French Doors

Seal the joints. Snip the end of the caulk tube at a 45-degree angle with a utility knife. Slide the tube into the caulk gun. Position the nozzle to direct caulk into the joints around the door frame, molding and around the edges of each lite, so all the joints are sealed. Squeeze the trigger gently to extrude the caulk. Run a bead of caulk along each side of the door and all sides of each lite. Run your finger along the beads to smooth the caulk into the joints. Caulk the remaining sides. Wipe off excess caulk with a damp cloth.

Weatherstrip the doors. Remove old weatherstripping from the header and door stop at the bottom of the frame, scraping and prying it off with a screwdriver, if necessary. Also remove old weatherstripping from the inside edge of the door panel -- one panel should have weatherstripping. Clean the surfaces to be restripped with a damp cloth. Allow the surfaces to dry. Measure the new stripping carefully and apply it according to the manufacturer's instructions. Confirm that the stripping material compresses and forms a tight seal when the doors are closed. Pay particular attention to the corners. Add a door sweep to the bottom interior edge of the door for additional protection against air exchange.

Insulate the glass. Install an insulating glass film on the interior side of each lite with a window insulating kit. Clean and dry the glass with a glass cleaner and lintless cloth. Measure the size of each lite. Cut a piece of film for each one, making the film 1 inch larger than the lite. Apply the enclosed tape to the edges of the first lite to be insulated. Peel away the paper liner to expose the tape’s adhesive. Adhere the film to the tape, smoothing out the film as you work. Blow-dry the film to smooth any wrinkles, beginning at one corner and working your way out. Trim excess film with a utility knife. The film can be peeled away when it's no longer needed or needs to be replaced.