Review on 🌡️ DIGITEN DTC151 Temperature Controller: Ultimate Plug-in Thermostat for Greenhouse, Reptiles, Homebrewing, and Aquariums - 110V 15A for Efficient Heating and Cooling by Jaime Bustamante

Most small electric heaters have a thermostat somewhere inside the case, so they don't keep a constant temperature very well. In this case, use a heater that does not turn off in the event of a power failure. They turn that heater on full blast so it won't turn itself off by its own thermostat. Then set the Digiten temperatures on and off. Then the heater maintains a very narrow range. I get about 1° or less deviation on the wireless indoor/outdoor thermometer unit a few feet away. When the weather gets colder you can switch the heating from low to high and the temperature stays the same. With a regular regulator on an electric heater, you have to turn it higher so that it stays on when going from low range to high range.