I have an attic fan with an old (MH Rhodes 90015 /marktime) mechanical timer switch. I want to replace the timer with a thermostat (presumably a line-voltage thermostat). To my surprise, in the switch box where I expected a line and load feed as in a typical light switch, the two wires that were attached to the timer are a line and a neutral with 120 volts. Is there a thermostat that would connect to that? Or will I have to find the junction box and rewire to convert the switch feeds to typical line and load?
There are line voltage thermostats, I use these for controlling electric heaters no battery a simple 2 pole switch with a temp dial. T522-w is the model I use 50-90 F temp range 120-240 at 22 amps 277v @ 18 amps I think it was close to 18$ at Platt but you may be able to find it cheaper online I believe when I ordered these there were some ~12$ but I needed 20 amp minimum 240V. , Added just checked online and you can find what you want using line voltage thermostat. Honeywell has one 13.95 (sold by Amazon) it's a 4 wire you only need to use 1 set, cap or tape the other set these are much heavier duty than your fan needs so they should last.
As @ThreePhaseEel points out you almost certainly do not have a neutral in the switch box. Therefore you cannot use any device in the box which requires a neutral. A line thermostat might be such a device. There may be battery powered thermostats which do not require a neutral.
I haven't lived in a house with an attic fan since childhood in Dallas TX in the 1950s. All it did was pull in 95 F air through the window next to my bed, and so I think a timer would be more useful for an attic fan than a thermostat. However, maybe in a locality where the temperature drops significantly and quickly after dark, then a thermostat would be useful.
I think that you would still need a switch in line with a thermostat because an attic fan on requires windows to be be open, doesn't it? And if everyone leaves the house, you would shut the windows, right? So you don't want the attic fan to come on when no one is there and the windows are shut.