Smoke stack with metal roof question

[Chickadee Acres]

Hi guys, new to the forum here. We are trying to finish up our new sugar shack and are stuck on the best way to seal the metal chimney to the metal roof. The smoke stack is single wall that transitions to double wall when it goes thru the roof. I have the standard metal roof jack and flashing from a stove shop. But when I went to Lowes to order the metal roofing, they guy suggested I use a hight temp silicone boot to seal the chimney. The boot is rated for 450 degrees and looks to be a cleaner install than the metal flashing with caulking. Has anyone used the silicone boot?

[maple flats]

Welcome aboard!
The stack on an evaporator will be far above 450 degrees in the inner stack. Check the ratings for the outer stack on the double wall you have. Stack temps on an evaporator at full boil will likely be in the 800-1200 or more. I used to see readings on mine even hotter before I added high pressure Air Over Fire (AOF). It is highly unlikely a beginner will have AOF.
Study to see if the ratings on your double wall show safe clearances. In general, adding a layer of tin (or SS) spaced out 1" on a non cumbustible spacer will cut the required clearance to combustibles to half. Unprotected wood (your building) needs 36" clearance, the double wall (unless that is insulated pipe) cuts that to 18". Another layer @ 1" cuts it to 9" and so forth. If it were me, I'd use the boot jack that you have. Then if any further sealant is needed, there are sealants rated at 700 degrees, some maybe even more.
You need to realize that an evaporator is not like a wood stove as far as stacks go. A woodstove is burned far cooler. An evaporator generally gets fueled every 7-9 minutes, with a whole arm load of wood and is made to burn as hot as you can get it, that's not the case with a wood stove, thus the stacks need better protection.

[Chickadee Acres]

Thanks for your input. The double wall pipe I am using is insulated and rated for 2" clearance. I like your idea of adding a layer of tin spaced out 1" to protect combustibles.

[buckeye gold]

I would not use the silicone boot, get a metal roof jack. a good shop can make you one. I had an Amish guy make me one from stainless steel liner pipe and built in a dead air space Box.

[foxtailsugary]

i have also been stuck on this as i am currently building my sugar shack. i have the high temp boot you are talking about and am going to give it a shot. i will let you know in a few weeks how it holds up when i cure my firebrick for new evaporator i just got.