In an effort to save some coin on our heating and cooling bills, I installed a programmable thermostat at the same time that we replaced our old, inefficient furnace with a new high-efficiency unit.
First off the new furnace is rated at 90% or higher efficiency. In fact it is so efficient that we no longer have exhaust going up the brick and steel chimney but rather out a plastic exhaust out the side of the house. So much of the heat is recovered from this exhaust that you can put your hand directly into the stream of exhaust and it only feels slightly warm where as the old furnace chimney would spew heat like crazy. That is money going out the chimney. I calculated that the money saved on energy would pay for the furnace in 5 years and after that the savings was money in our pockets.
What about the programmable thermostat?
I guess I get the idea that if you are not heating when you don't have to you will save energy but does that work out in reality? Seems that the overwhelming opinions of experts is that programmable thermostats will save energy if they are used properly.
So how to use it properly?
What I found was this: for every 1 degree F that you reduce the temperature over an 8 hour period will reduce the amount of gas you use by 1%. So if you can turn down the heat by 10 degrees for 8 hours per night when you are sleeping it should save 10%, More even, if you can let the temperature drop again during the day when everyone is gone, however a lot of families have someone home all day so this is not always possible.
The trick is to lower the temperature for as long of a period of time as possible because the smaller the difference between the inside temp and outdoor temp is, the less energy your house will lose. Of course, the better insulated your house is, the longer that it will take for the temperature to drop down even after the furnace is not putting out, and consequently it will reheat faster once the furnace kicks in again.
While researching what was the best way to set up my programmable thermostat, I read some opinions that it takes more energy to recover to the comfortable temperature after letting the temperature drop than it is just to maintain a constant setting. Research done by several studies indicates that this is not true and that as long as you don't try to micro manage the temperature up and down and especially don't over compensate to the high side then the programmable thermostat will do a good job of saving energy and money.
To get back to the question of how much difference that installing a programmable thermostat can make, a study of 400 homes that had one installed without any other upgrade to the heating system saved an average of 6.2% on the old gas consumption. A higher savings was realized in more severe climates than in more temperate areas.
Bottom line - They are easy to use, simple to install and save money!