I used this trick a few years back during a cold snap when my furnace wasnt working. It did genuinely increase seem to increase the temp of my room by around ~10 Fahrenheit over an hour or so.

my understanding was capturing the hot air for a moment allowed more heat to radiate (and the pot did genuinely get to around 150 degrees according to laser thermometer) instead of the hot air rising in a narrow stream and losing its heat into the cold ceiling.