Steam hoods, forced air and pre-heaters... its all about getting the most out of the fuel and time you spend in the sugar shack. Steam hoods help keep drafts off the surface of the sap, keeps the heat in, gives you distilled hot water supply (we use it to heat our cans of soup for lunchtime)and gets the steam (actually, condensed water vapor) out. Forced air would be my next choice, as it pushes the heat/flames along the whole length of your arch and greatly reduces the build-up of coals and ashes. The preheater utilizes the free heat in the steam hoods to take the chill off the sap; just make sure you have a drip pan to capture the condensing water with a drain to get it out as well... another hot water source. I remember hand-dipping cold sap from the storage tank into our flat pan system years ago, and how discouraging it was when the cold sap killed the boil. Same deal without the preheater, however you don't see the effect to the same extent in a flue pan. With the preheater, we have had a full boil in the flue pan from front to back and side to side. And yes, you still need to watch for foaming with a preheater.
Mount View Sugar Bush - Since 1989
2004 5.5' x 18' Custom-built Stainless Evaporator w/ 7' Piggyback + Preheater
4,000 - 5,000 taps vacuum/gravity/bags
24' x 32' Sugar Shack