Mark writes:
I have an insulated garage that I want to heat, but just above
freezing. All the heaters I have will keep the temperature at 14C
(57F) or higher, which I don't want. I just want it slightly above 0C
(32F) to avoid the objects in the garage from freezing.

Does anyone know of such a heater? I can't seem to find one.

Look at electric baseboard heaters. These are normally supplied from
240 V, so you can get several kW of heat from ordinary 14 ga wiring.

Most makes of baseboard heaters seem to have auxiliary thermostats
that you can install inside the wiring box at one end of the baseboard
unit, with the temperature-setting knob sticking out through some kind
of knockout. If you look closely, you'll probably find that there are
two different models of this thermostat offered. One model has an "off"
position, allowing you to turn off the heater entirely. The other model
does not have an "off" position, and it's deliberately calibrated so
that if you set it to the minimum temperature, it will come on about 4
degrees C (about 39 degrees F). That's what you want.

Dave