stove pipe temp?

[softmaple]

what would be the average stove pipe temp on the outside be if i had a double walled stove pipe and a inside stack temp of around 550degrees if i had my evaporator up and ready i would test it myself but i dont at this time its would be a round figure i understand.

[Fred Henderson]

There are a lot of variables here to be considered, such as the air temps that given day.

[softmaple]

what i'm thinking of is adding a stove pipe preheater around the stack of the double walled insulated pipe. now i know that the pipe will hold back a heck of alot of heat, but i dont want to boil the sap in the pipe either. maybe a couple of 3/4 inch pipe following the stack parallel to it, like the preheaters in the pans do, but vertical and hugging the pipe around 3 feet long or so.

[maple flats]

Some guys have made preheaters around single walled stacks open to the air and have actually boiled sap in it. Check with Johnny Cuervo (member # 255 in membership list). He has good pictures and explanations of what and how he did one. The heat potential is pretty high, no need to further shield a preheater to get enough heat but it should have direct contact according to Johnny. You can check his old posts and he gives full details.
Dave

PS, In the woodstove heating business every time you add a layer of sheet metal spaced out an inch you cut the clearance needed in half, so if you have info that you need 36", 1 x layer=18, second x layer=9, 3rd x layer=4.5" I am not sure your 36" is right to begin, reasearh may be needed. Or a x layer with ceramic blanket between that layer and the wood should be quite good, in other words, stack pipe inside a second layer spaced 1" out and then the blanket.