I have a radiant tube heater that currently has an old Honeywell thermostat:
You’ll notice that there are no switches on this thermostat…it’s strictly a line-level switch. No on/off, no heat/cool, no auto/off, etc. It’s wired inline with the 120VAC load side.
I tried a Stelpro STZW402+ but that doesn’t work. I need something that is strictly a thermostatically controlled on/off switch.