There are two main vacuum oven heat methods:
1 Radiant, where the inner walls are heated by attached heaters, and the infrared energy bounces around the chamber to be absorbed by what you’re trying to purge.
2 Individually heated shelves, where heaters and thermocouple sensors are encased in each shelf, each with its own PID temperature controller, in this case what you’re trying to purge comes into direct contact with the heat source.
The radiant heat vac ovens need a double wall, the inner wall gets hot, and for safety reasons it should be isolated, also the inner wall needs to be insulated from the outside air to maintain its temperature stability.
But an individually heated shelf vac oven doesn’t have any need for the outer wall!! I’ve posted up repeatedly at ICMAG Forums about this, and have made my case to Across International a couple of times face to face at the cannabis oil festivals.
All you need is a sturdy box that can withstand vacuum.
Secondly, the way they heat the shelves can be way improved upon with little increase in cost compared to the huge prices they ask for these things. Instead of incasing a crude metal heating element in a pocket within the shelf, just use a plain sheet of aluminum or stainless steel for the shelf, and stick a full width and depth silicone heater (heat mat) with attached sensor to the bottom. The silicone heaters can be ordered from Keenova with 3M adhesive backing (simply peel off the protective layer and stick the heater to the bottom of the shelf.) Keenova will also attach a thermocouple to the center of the heater if you want.
Here’s Keenova’s custom silicone heater page at eBay to show you how simple this all is…
I’ve ordered silicone heaters from Keenova with no problems, as described with quick delivery. I have a couple sitting around still waiting to be purposed.
Btw, Best Value Vacs took my stock pot vac chamber heater design which I originally posted up at Toke City Forums, and has been making a profit off it for several years, they call them Digital Heatpads, here’s a link,
I haven’t asked for a dime for my contributions and never will.