I wrote about this in an earlier post, but I thought I could expand on the information a little bit. We have three heating zones in our house, each is controlled by a programmable thermostat. By installing the programmable thermostats, I believe we have saved about 15 to 20 percent on our heating bills.

The installation was very straight forward. Most oil and gas furnaces have a small 24 V AC transformer mounted near the burner. This supplies the power to the thermostat circuit that tells the furnace to turn on and off. For most thermostats, there will be a red and white wire attached to the thermostat, which runs down to the boiler controller. They don’t have to be red and white, but that is the standard colors that are used in most installations.

Non-powered thermostats will have a coil of metal attached to a glass tube with a small amount of mercury in it. as the temperature goes down, the coil will unwind, causing the mercury tube to tilt. Since mercury is a metal, it conducts electricity, so the tube tilting one way completes the thermostat circuit and turns on the furnace. Tilting it back the other way breaks the circuit and turns off the furnace. Pretty easy, right? When you discard your old thermostat, make sure to do it properly so we don’t end up with a bunch of mercury in our land fills.

A powered thermostat works using electronic circuits and a small relay to turn the furnace on an off. The power for a thermostat usually comes from batteries, but there are some units that will run on the 24 VAC supply from the furnace. Those are mostly commercial type units, but occasionally they can be found if you don’t like changing batteries once a year. The same wire colors are used for both powered and unpowered thermostats, red and white. Where this can get confusing is if you have a central AC system because they will have a second set of wires to run the AC compressor. The AC unit wires are normally Green and Yellow, but once again, they can be any color if the installer was not paying attention or following industry standards.

When installing our Honeywell CT3500, I used the mounting template provide by the manufacture. Since I ran the thermostat wire myself, I knew basically where the wall stud was located (right next the the hole the wire came through) so a managed to get one of the screws securely into the stud. I leveled the unit an then used one of the dry wall anchors to secure the other screw. The installation was pretty easy, all in all.

Then I programmed each unit. Programming detail vary from thermostat to thermostat, so I won’t go into great detail on how I did it. Our thermostats have four dayparts: Wake, leave, return, sleep. I programmed each zone a little differently:

Zone 1 is the two small bedrooms and old bathroom. This is where our daughter sleeps, so I like to keep it a little warmer at night. Zone 2 is the master bedroom. I like to sleep in the cold, in fact, I would like to sleep with the window open, but I had to compromise on that with my wife. Zone 3 is the great room, which has the wood stove. When the wood stove is running, that zone never needs heat. I programmed all of the days the same, since my wife is a stay at home mom.

It is nice to wake up to the house getting warm all by itself. By the time I get out of bed at 6:20 or so, the temperature is already at 69 degrees.

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