I am putting in a gas log set and have a Milliamp Thermostat. I have a separate fan from my fire place that I can turn on and off by a switch. I would like to have the Thermostat automaticaly turn on the fan when it turns on the burners for the gas logs. Is there a switch or really that I can add to the on off switch so that if it is set to the on position the thermostat would control the fan.

A few problems associated with what you want to do.

Milliamp wiring does not like and other wires around its thermostat wiring. Reason? The millivolt power signal is VERY weak and bleeds off in a short distance and metallic wire no matter if it is insulated or not will have a power signal drawing effect on the signal from the millivolt generator.

All thermostats I know of are designed to use one voltage style at a time so any combination will not work.

You might be able to install a heat sensing disc along the power wires for the fan motor. As the heat of the unit comes to temperature the disc will close and the fan will start running. It will be automatic but will not activate immediately upon heater activation.

I am sure there are other ways to get the job done but all the designs will have to be done and tested by you unless you can find a wiring diagram from another brand of unit that has the blower operation combined another way.

Have fun with your project.

With the right selection of parts you should be able to do it.

In reality, you need two sets of thermostat contacts, a 24 VAC transformer and a contactor for the fan and a 24 VAC fuse.

One relay for the millivolt signal should be as close as possible to the millivolt generator.

The other runs the contactor for the fan.

You should be able to set a thermostat to electric heat and have independent control of the fan (G and C) controls the Fan and (W and C) controls the gas millivolt contact via SEPARATELY activated relays. Coils go to G and C and W and C; R goes to other side of the secondary.

When a thermostat is set to electric heat mode, the thermostat controls the fan.