Just into the syrup. To keep away from the sugar sand just keep the temperature at 185-190 max. The electric can do that quite well. I'm not sure about using a propane flame under a WJ unit, check with the manufacturer. I wonder if the flame so close to the element, even though the element is in water, might somehow damage the element. I'm not saying it will, I just wonder. Whoever made the canner will need to answer that. Even a small element will get the whole contents to the right temp, as long as the t-stat is set right, it will just take more time than a bigger element.
Once you use a WJ canner you will never want to go back to propane fired.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.