Line voltage thermostat to shut off attic fan when outside temp is close to inside


I have an attic fan with a thermostat, but with the high heat these past weeks, the outdoor temperature is often above the thermostat setting. Thus, I'm just replacing all the air in the attic with more hot air from outside the attic, at the same temperature. Its a huge waste of electricity.

I'd really like to find a thermostat that will compare the outside temp to the inside one, and shut off the fan only if the temperature inside is w/in 5 degrees or so of the outside temperature.

Does such a product exist?

Best Answer

The only easy way (and non dynamic) is to have an external temp switch that turns on the internal main switch. Or the other way around depends how you want it to work.

Outside 35Degrees Inside 25 Degrees External >30(OFF) --> Internal >20(ON) --> FAN OFF

Outside 20 Degrees Inside 25 Degrees External <30(ON) --> Internal >20(ON) --> FAN ON

My logic might be slighltly flawed but its the only way I can think of. Otherwise you have to buy some more inteligent system (usually expensive) or make your own microcontroller based relay

A Thermostat With Adjustable Hysteresis