110V relay help

You need an Opto-Isolating Triac, this will safely isolate the low voltage side form the high voltage side.
Do an internet search for opto-isolating triacs, get the data sheet on a suitable one and there may be circuits in the application notes.
Make sure you get your work checked by somebody who knows what they are doing before you build it and definately before you plug it in.

 

For someone who seems new to electricity as does the OP I would recommend starting with the low-tech approach of a plain old relay. I haven't looked for a while, but I suspect Radio Shack has exactly the device you need.

 

An lm35 temp sensor hooked up to a comparator to trigger a relay is probably the way I would go. You can hook a pot up to the comparator to adjust the reference voltage and act like a thermostat. The last time I used an LM35, I believe it sourced 1mA/degree Celcius.

 

I don't think you want to put line voltage on your temp. control wires. As Averagesupernova says; use a "plain old relay" ...that can be mounted on the fan with the other power devices.

 

When you wire a line votage thermostat, you wire it as in place of a wall switch.
If the fan has a wall switch in a sutible location, you can just substitute.

 

"When you wire a line votage thermostat, you wire it as in place of a wall switch."

Okay then.

I wanted to make sure that the OP didn't try to wire line voltage to his existing thermostat.

 

Good point.

It's also not trivial to design a safe low voltage controller.
Proper enclosure and isolation layouts are not something to attempt without expert knowledge.

Better off purchasing a suitable UL approved controller.