Is there a straightforward way to add a thermostat to an existing (basic no-frills) whole-house fan? I'd like to be able to set it to shut off when the outside temp rises to a certain point--so that the fan shuts off automatically in the early morning.

A simple timer would probably be fine. Could the fan easily be wired to an off-the-shelf HVAC thermostat? (...and program the thermostat to turn off the fan at X a.m. if the indoor temp is above 0 degrees, say...) There is an existing central HVAC thermostat that could be replaced or added to if needed.

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    Is your fan hard-wired or plugged into an outlet? – isherwood Jul 12 '16 at 21:08
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    Shouldn't be too hard if you use a line voltage thermostat. – Tester101 Jul 12 '16 at 21:30
  • @isherwood, it's hard wired... – Phil Esra Jul 12 '16 at 22:15
  • @Tester101, interesting, I didn't know you could get a programmable line-voltage thermostat...I've found them online now after a specific search. – Phil Esra Jul 12 '16 at 22:28
  • Huh, this timer (designed for a receptacle box) might be a fairly simple solution--the timing is probably the more critical piece (vs temp), since I can assume the fan will need to shut off around dawn, plus or minus: homedepot.com/p/… – Phil Esra Jul 12 '16 at 22:39

If you just want a timer, it's easy to buy a line-voltage timer switch that you can drop-in where the current fan's on/off switch resides.

If you want a thermostat, as the comments said you can find a line-voltage thermostat. THen you just need to run the hot feed from the on/off switch to the hermostat and then on to the fan.

Another option would be to use any low-voltage thermostat in combination with a 120VAC relay, but then you've got more parts, and need a low-V supply for the thermostat, so I wouldn't choose this option :-)

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