This method Ryan recommends is to keep the tree out of dormancy at 70-80F thermostat setting for one year to give it a boost. The next year the tree needs to be dormant. So
That said, one can use the exact same set up as Ryan with a thermostat setting of 40F and keep the tree in dormancy, but roots above freezing. If this is the method chosen, it is important to choose the correct thermostat, a thermostat whose range is at least 25F and up to assure the thermostat isn't working at the bottom of its effective range. Some hobby thermostats lowest effective range is 40F.
Both the Inkbird temperature controller I mentioned earlier and the one JudyB is using (which governs both heating and cooling) will do this:
bayite Temperature Controller BTC201 10A Dual Pre-Wired Digital Outlet Thermostat Plug, 2 Stage Heating and Cooling Mode, 110V - 240V.
Cheers
DSD sends