Move it first. If you can't easily heat the sugar house just put a small heat source in the firebox. Can you run a light bulb there? I did mine using my generator and putting a 100 watt bulb in the firebox, that kept it from freezing. Then on day 2 or 3, light a small fire in the arch, let it burn out and after cooling but before freezing, put the bulb back in. Repeat for about 3-4 days, each time firing the arch a little hotter, but don't go all out until at least 3 preferably 4 days of firing. Refractory does not cure like regular mortar or concrete, it needs heat. Just don't rush it. By the 4th day, you could fire it for about 60-90 minutes, but still with just a medium fire. The longer you take to cure the refractory, the better it will last, if rushed you will end up with a lot of cracks and some loose chunks will break loose.
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.