Home thermostat question

This may be an odd question to ask here at the SD, but we have some pretty darn smart people here so I thought I would ask.

The wife and I want to install one of those thermostats that you can program to go to a specific temp at a specific time and such. All of the ones that we have seen in the store have a 4 wire connection (EASY 4 WIRE CONNECTION!!! the packages exclaim) but our thermostat only has 2 wires. I gather so the furnace is either on or off (open/closed circut). The one we have now is a plain jane honeywell with a mercury switch on a slider that I believe most people probably have.

Does anyone know if I can hook/adapt a 4 wire job to mine? I just want it to turn the furnace on/off at a specific time to a specific temp. I don’t care about other features like just blowing the fan with no heat for air circulation.


PS - We have a Natural Gas furnace, and yes I asked staff at the store for help. No joy.

The four-wire ones control the A/C and the heat. I assume you would only use one pair of wires.

You may want to check into a “heat only” model.

You’ll probably be OK; check the installation instructions. Most describe how to make 2-wire connections.

Did you know if you connect the two wires to each other the furnace goes on?

Those store clerks shold have opened it for you so you could see the instructions. Try another store.

Thanks for the responses. They all sound probable. You bet Handy, connect them, the circut is closed and the furnace goes on. Simple as that. So, I just have to figure out which one of the 3 other wires (I gather the green will be earth, correct?) is the furnace/heat wire. I will crack one open and read the instructions after work… then I guess it should be safe just to ignore the others, after all I think it is powered by a 9V battery so I shouldn’t have to worry about power arcing all over the place.

The four wires ont a thermostat control both the A/C and Heat. The red and White(or green sometimes) are the ones connected to your furnace whereas the yellow and blue are for the A/C. Basically all you have to do is check the connection at the furnace, and hook up the two wires to red and white (green) on teh thermostat. Hopefully your current wires are color coded like that. If not at your furnace the wires are hooked up to a letter i.e. R for red. bla bla, i think you get teh idea. Just match 'em. Enjoy the new thermostat

Red is the 24v “hot” or power from the transformer.
White is the common from the transformer.
Green goes to the fan controls.
Blue or Yellow is for cooling use.
Think of your Tstat as ,basically, a switch.When the desired temp (setpoint) is reached (+/- the deadband) it opens the switch.This removes 24VAC from the control circuit which causes the gas valve to close and turns off the fan after a cooldown period.

As said before match the color of the wire insulation to the letter on the screw terminals and you should be fine.