How can I predict now the heat sinks that will appear in winter?
The general principle to use is that actual air leaks are a lot worse than just having poor insulation.

Look around your doors, windows, plumbing, attic/basement/crawlspace access hatches, fireplace, and anywhere else where there's a hole in the wall. Anywhere you feel air movement is an issue. Anywhere you can see daylight (that's not glass) is an issue.