Dear Jim: I wonder if installing a programmable thermostat myself really will save much money? I heard it is best to leave the temperature constant. With so many models available, how do I select among them all? – Pat W.

Dear Pat: Replacing your old thermostat with a programmable (smart) model provides the best return of any investment you can make in your home. Even a simple low-cost model, less than $25, can easily pay back its cost within a month and save more than $1,000 throughout its life.

Installing a smart thermostat makes sense from comfort and convenience standpoints, even if it did not cut your utility bills. These thermostats keep the indoor temperature steady and at precisely your desired setting. Older thermostats are very inaccurate.

It is a common misconception that setting your thermostat lower and then back up later uses more energy. Overall, the furnace runs fewer minutes each day when the thermostat is set back when you are gone and turned back up when you return.

Even if you are home all day, there are times when the indoor temperature can be comfortably cooler for savings. For example, when you are sleeping at night, cooking dinner, washing clothes, exercising or doing other vigorous activities, your house does not have to be kept toasty warm.

A programmable thermostat automatically makes these temperature changes for you. It is called smart because its computer brain knows precisely when to start the furnace. If you awake at 6:30 a.m., it starts the furnace a bit earlier so you never even know the room temperature was lower overnight.

When selecting a programmable thermostat, look for a minimum of four different possible time-temperature periods per day. They are often called wake, day, evening and sleep. Features such as a temporary override, program lock (so your children can’t change it), an air filter monitor, and a temperature swing adjustment are pluses.

Depending on your family’s activity schedule and your budget, you can select from three basic types: 7-day, 5-1-1, and 5-2. A 7-day model allows you to program a different time-temperature schedule for every day.

A 5-1-1 model provides identical schedules for each weekday and different ones for Saturday and Sunday. A 5-2 model is similar except both weekend days have the same schedule. A 5-2 is adequate for most families. If you have a heat pump with backup heat, you must select a heat pump model.

A programmable thermostat is not difficult to install yourself. All the wires are a safe low-voltage and they are color-coded. Many models come preprogrammed with a typical schedule. You can use it immediately by just setting the current time and personalize the schedule later.

Write for (instantly download – www.dulley.com) Update Bulletin No. 850 – buyer’s guide of the 11 programmable thermostat manufacturers (24 models) listing programming options, time-temperature schedules, comfort-convenience features, and a setback saving charts. Please include $3 and business-size SASE, and send to James Dulley, 6906 Royalgreen Dr., Cincinnati, Ohio 45244.