How to program a thermostat: schedules, periods and hold

The three kinds of thermostat schedule

ENERGY STAR's 2009 heating and cooling guide describes three kinds of programmable thermostat. A 7-day model lets you set a different program for each day of the week. The guide says that suits a household whose daily schedule tends to change.

A 5+2 model uses one schedule every weekday and another for the weekend. The guide says 5-1-1 models are best if you tend to keep one schedule Monday through Friday and another on Saturdays and Sundays. The guide says a 7-day model usually has four possible temperature periods per day.

The Honeywell RTH2300 manual describes a 5+2 model. It says the same settings are used every day from Monday to Friday, and another set is used for Saturday and Sunday. Its example programs all four periods on weekdays but only Wake and Sleep on weekends.

UF/IFAS Extension, the University of Florida's extension service, says a programmable thermostat can store and repeat multiple daily settings.

Step one: set the clock and the day

On the RTH2300, you press Set, use the Up or Down button to set the time, press Set again, and choose the day. Pressing Run saves the change.

That manual says a flashing time display means the clock has lost its settings. If the thermostat is following the schedule, it uses the weekday Wake settings until you reset the clock. The RTH6500WF user guide gives a similar warning about a flashing Set Clock message.

A 2011 article from Lawrence Berkeley National Laboratory described a small survey of thermostats. It found that some homes had the wrong time of day on the thermostat's clock. The article says a wrong clock negates the programming.

Honeywell says the RTH6500WF, when on Wi-Fi, shows the local time based on the account holder's zip code. Without Wi-Fi, its clock is set on the thermostat's own screen. Our guide on how to reset a thermostat covers blank or frozen screens.

Step two: give each period a start time and a temperature

The RTH2300 manual lists four periods. Wake starts when you wake up. Leave starts when you leave for work. Return starts when you return home. Sleep starts when you go to sleep.

The manual says each period needs a start time and two temperature settings. One is used when the thermostat is in cooling mode, and one when it is in heating mode. To set the cooling temperature, it says to put the System switch in Cool first. The manual says the System switch places the system in Cool, Off or Heat mode. For heating, put it in Heat.

On the RTH6500WF, you press Set Clock/Day/Schedule, then Set Schedule. You set Monday's Wake time, then its temperature, then move to Leave and the later periods. You repeat this for each day and press Done to save.

The RTH2300 lets you skip any period except Wake. You hold the Hold button for 4 seconds while that period is shown. It also saves your changes if you press nothing for 60 seconds.

Both Honeywell models come preset. The RTH6500WF user guide lists default cooling settings of 78° for Wake, 85° for Leave, 78° for Return and 82° for Sleep. You can keep those or change them.

Temporary hold, permanent hold and getting back to the schedule

A temporary hold, also called a temporary override, changes the temperature only until the next period starts. On the RTH2300, you press Up or Down, and the word Temporary appears. The RTH6500WF user guide says pressing Cancel brings the schedule back sooner.

A permanent hold keeps one temperature until you end it. The RTH6500WF user guide says pressing HOLD will turn off the program schedule. The temperature you set is kept 24 hours a day until you change it or press Cancel.

On the Honeywell TH6320ZW, you press Hold Until and then choose Permanent Hold. To go back, you choose Run Schedule. Honeywell says the screen then shows Following Schedule.

ENERGY STAR's guide says to set the hold button at a constant energy-saving temperature when you go away for the weekend or on vacation. It also says to resist the urge to override the pre-programmed settings.

The 2011 Berkeley Lab article says one survey found half of the homes had their thermostats on long-term hold. It says that erases the energy efficiency benefits of programming, because the temperature stays the same no matter the day or time.

Early start, special models and where the thermostat sits

Some thermostats start heating or cooling before a period begins. Honeywell calls this Smart Response Technology. The RTH6500WF user guide says the thermostat learns how long your system takes to reach the setting, so the temperature is reached at the time you set. The screen shows Recovery while it does this.

A heat pump is a system that provides both heating and cooling in one integrated system, in ENERGY STAR's words. The Department of Energy says programmable thermostats have generally not been recommended for heat pump systems. It adds that some companies now sell programmable thermostats made for heat pumps. ENERGY STAR says a heat pump may need a special programmable thermostat to maximize energy savings year-round, and to talk to your retailer or contractor first.

ENERGY STAR also says the thermostat should be away from registers, appliances, lighting, doorways, windows and direct sun. It says interior walls are best. If yours sits in a bad spot, moving it is a job for a licensed contractor.

Batteries and a yearly check

Some programmable thermostats run on batteries. ENERGY STAR says to change them each year if yours does, and notes that some units show when they need changing.

The RTH2300 manual says Lo Batt appears on the screen 60 days before the batteries run out. It says to replace them once a year, or when you will be away for more than a month. It also says to set the System switch to Off before removing the batteries. Otherwise the heating or cooling system could stay on.

That manual says most settings are kept in permanent memory. After new batteries, only the clock and the day need to be set again.

ENERGY STAR's guide says your contractor should check thermostat settings each spring and fall. The check makes sure the system turns on and off at the programmed temperatures. For how a thermostat signals your equipment, see how a thermostat works. If the screen stays blank or the settings keep vanishing, see signs a thermostat is going bad.