Anyone ever fitted engine ducting for the heater?

Just a thought, as I have some alloy ducting used for a kitchen extractor. I was thinking I could cut it to make it fit between the intake and exhaust manifolds, with one end getting an airflow from the engine fan, and the other feeding into the heater fan intake. Increased airflow and warmth. Daft?

This is a bit like what we did on tractors years ago,canvas down each side of the engine directing some warmth at the driver. There are better less dodgy ways of improving things today.