Or there is more than one physical effect in play: see https://news.ycombinator.com/item?id=8112118 https://news.ycombinator.com/item?id=8112118 -- there's air

Or there is more than one physical effect in play: see https://news.ycombinator.com/item?id=8112118 https://news.ycombinator.com/item?id=8112118 -- there's air movement as well as heat, because your house is not a sealed box.