Hi @Grant-noclue,
Thank you for your question about sealing up your french doors to help reduce the cold air transfer.
To keep the cold air out, you'll want to do your best to seal up any gaps that are letting it in.
The best thing you can do is add Self Adhesive Window and Door Weather Strips at all the areas where the doors contact each other and the frame. When closed against the foam strips, they will compress and create an airtight seal that will prevent cold air transfer.
Additionally, you can place Draught Stoppers against the base of the doors when they are closed to prevent air from travelling underneath the doors.
You could also consider adding some curtains over the doors as they will help to insulate the opening that little bit extra.
You might like to check out How To Winter-Proof Your Home and Six Ways to Weatherproof Your Home For Winter for some further tips.
Let me know what you think.
Jacob
