Grit only works down to -6 apparently. We had temps down to -20 here last winter!
I would seriously think hard about winter working if this big investment is being based on it.
I fitted a 3Kw, 27" immersion heater to my tank in January so I've worked with hot water, albeit, not boiling, but hot & I found that there is a limit to what you can still work with. I found that between about +2 & -3 the heated water was of huge benefit. From -4 & below the water still froze on the glass & everywhere else.