• electromechanical,
• digital,
• hybrid,
• occupancy, and
• light sensing.

Most range in price from $30 to $100, except for occupancy and light sensing thermostats, which cost around $200.

Electromechanical - Electromechanical (EM) thermostats, usually the easiest devices to operate, typically have manual controls such as movable tabs to set a rotary timer and sliding levers for night and day temperature settings. These thermostats work with most conventional heating and cooling systems, except heat pumps. EM controls have limited flexibility and can store only the same settings for each day, although at least one manufacturer has a model with separate settings for each day of the week. EM thermostats are best suited for people with regular schedules.

Digital - Digital thermostats are identified by their LED or LCD digital readout and data entry pads or buttons. They offer the widest range of features and flexibility, and digital thermostats can be used with most heating and cooling systems. They provide precise temperature control, and they permit custom scheduling. Programming some models can be fairly complicated; make sure you are comfortable with the functions and operation of the thermostat you choose. Remember— you won't save energy if you don't set the controls or you set them incorrectly.

Hybrid - Hybrid systems combine the technology of digital controls with manual slides and knobs to simplify use and maintain flexibility. Hybrid models are available for most systems, including heat pumps.

Occupancy - Occupancy thermostats maintain the setback temperature until someone presses a button to call for heating or cooling. They do not rely on the time of day. The ensuing preset "comfort period" lasts from 30 minutes to 12 hours, depending on how you've set the thermostat. Then, the temperature returns to the setback level. These units offer the ultimate in simplicity, but lack flexibility. Occupancy thermostats are best suited for spaces that remain unoccupied for long periods of time.

Light Sensing - Light sensing heat thermostats rely on the lighting level preset by the owner to activate heating systems. When lighting is reduced, a photocell inside the thermostat senses unoccupied conditions and allows space temperatures to fall 10° below the occupied temperature setting. When lighting levels increase to normal, temperatures automatically adjust to comfort conditions. These units do not require batteries or programming and reset themselves after power failures. Light sensing thermostats are designed primarily for stores and offices where occupancy determines lighting requirements, and therefore heating requirements.

Choosing a Programmable Thermostat
Because programmable thermostats are a relatively new technology, you should learn as much as you can before selecting a unit. When shopping for a thermostat, bring information with you about your current unit, including the brand and model number. Also, ask these questions before buying a thermostat:

• Does the unit's clock draw its power from the heating systems's low-voltage electrical control circuit instead of a battery? If so, is the clock disrupted when the furnace cycles on and off? Battery-operated, back-up thermostats are preferred by many homeowners.
• Is the thermostat compatible with the electrical wiring found in your current unit?
• Are you able to install it yourself, or should you hire an electrician or a heating, ventilation, and air conditioning (HVAC) contractor?
• How precise is the thermostat?
• Are the programming instructions easy to understand and remember? Some thermostats have the instructions printed on the cover or inside the housing box. Otherwise, will you have to consult the instruction booklet every time you want to change the setback times?