Convention dictates reducing standard oven temperatures by 20°C when using a fan oven. This makes tolerable sense for moderate temperatures and cooking times but for slow cooking at low temperatures it appears to be illogical. The effect of more efficient fan-assisted heat transfer must become irrelevant after an hour or two, and if a recipe suggests 110°C then setting a fan oven to 90°C (below boiling point) could give very different results. Should we correct for this?