Pre-heated air?

[Petter]

I am woundering if anyone has experience from using pre-heated air, like a steel tube entering though a closed oven door and exit into the fire/embers. Pre-heated primary air increase burning efficiency. You loose heat up the chimeny as a result of the the air excess if the opening/door is fully open. Think of a modern stove compared to a open fire to heat a home.

Once the oven is hot, the tube and door is removed and the rest is as usual.

Thanks
/Petter