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Set a thermostat schedule by choosing one temperature for the hours the household is home and awake, a setback for sleep and for the hours the house is empty, and entering those periods for weekdays and weekends. Then leave it alone for a week before adjusting anything. For a furnace or a central air conditioner, the setback is where the saving is. For a heat pump the rule is different: one comfortable temperature, held, because a setback can trigger the backup heat.
A setback is a period when the thermostat holds the house cooler in winter, or warmer in summer, than you would want while sitting in it. A programmable thermostat repeats setbacks on a weekly clock; a smart thermostat learns them or senses when the house is empty.
Why does a schedule matter?
A schedule matters because heating and cooling is the largest slice of most energy bills, and the house does not need to be comfortable at four in the morning or at noon on a workday. ENERGY STAR's page on smart thermostats says that for the average American household, almost half of the annual energy bill goes to heating and cooling. A thermostat that sets back on its own captures the empty hours without anyone remembering to touch it.
The Department of Energy's home energy checklist says to install a programmable thermostat to set back automatically at night, and that heating can account for almost half of the average family's winter energy bill.
How often should you revisit the schedule?
Revisit the schedule twice a year, when the system switches from heating to cooling and back, and whenever the household's pattern changes: a new job, a child home for the summer, someone now working from the house. A schedule written for last year's routine sets the house back while people are sitting in it, and they override it, which is how most schedules die. The mode switch is also a good moment to change the filter.
| Period | Furnace or air conditioner | Heat pump |
|---|---|---|
| Wake | Home temperature | One held temperature |
| Away (workday) | Setback | Same held temperature |
| Home (evening) | Home temperature | Same held temperature |
| Sleep | Setback | Same held temperature |
What do you need?
You need the thermostat's manual (or its model number, printed inside the cover, to find the manual online), a written note of the household's weekly pattern, and your equipment type: a furnace with a separate air conditioner, or a heat pump. If the thermostat is being replaced, add a small screwdriver, a phone photo of the old wiring, and the location of the air handler's breaker.
- The thermostat manual, or the model number from inside the cover
- The equipment type: furnace and AC, or heat pump (a heat pump's outdoor unit runs in winter)
- A week of notes on when the house is empty, awake, and asleep
- For a new thermostat: a photo of the wiring before any wire comes off, and the breaker for the air handler
What are the steps?
Confirm the equipment type, write down the weekly pattern, choose the two temperatures, enter the weekday periods, copy them to the weekend and adjust, set the fan to auto and the mode to heat or cool, then live with it for a week before changing one thing at a time. Write the settings down at the end.
- Confirm what the thermostat controls. A heat pump thermostat usually shows an "emergency heat" or "aux" option, and the outdoor unit runs in winter. If it is a heat pump, skip the setbacks: pick one temperature, go to step 6, and read winter care for a heat pump for why.
- Write the weekly pattern: when the first person gets up, when the house empties, when someone returns, and bedtime, for weekdays and weekends separately.
- Pick the home temperature by comfort, not by a rule, then a setback a few degrees off it for sleep and away. The Building America Solution Center's smart thermostat guide uses the example of a setback to 68 F overnight, back to 72 F by 7 AM, and notes a learning thermostat starts recovery early to hit that time.
- Enter the weekday periods: wake at the home temperature, leave at the setback, return at the home temperature, sleep at the setback.
- Copy the weekday program to the weekend, then move wake and leave later, or delete the away period if someone is home. Done when: every period on every day has a temperature you chose on purpose.
- Set the fan to auto. ENERGY STAR's page on air-source heat pumps says to use the auto fan setting or the lowest speed that spreads the air enough. In practice, a fan left on also blows moisture off a wet air conditioner coil back into the house.
- Set the mode to heat or cool for the season rather than auto. The same ENERGY STAR page says this avoids mode switching on unseasonable days.
- Live with it for a week. If someone keeps overriding one period, the setback is too deep or the time is wrong. Change one thing, then wait another week. Done when: a week passes with no overrides.
- Write the final schedule down: each period, its time, its temperature, and today's date.
When should you stop and call a pro?
Call an HVAC technician or an electrician if the wall has more or fewer wires than a new thermostat expects, if the thermostat runs electric baseboard heaters (line voltage, not the low-voltage circuit a programmable thermostat is built for), or if the system short-cycles or the backup heat runs constantly after a change. The Building America Solution Center's guide says most smart thermostats need a 24 VAC circuit with four available wires, and to call an electrician if you do not feel comfortable with electric wiring.
If the complaint is that upstairs is hot while downstairs is cold, the thermostat is the wrong suspect. The same guide puts large floor-to-floor differences down to ducts, returns, insulation, air leakage, windows, or shade; sealing the ducts you can reach is the first thing to try.
What should you record?
Record the schedule itself (each period, its time, and its temperature), the thermostat model, the date you set it, and the equipment it controls. Keep the twice-a-year review on a recurring schedule beside the filter change, with the settings in the task's notes on the home record. The utility bills are the other half of the record; a maintenance budget built from real bills is how you learn whether a change did anything.
Common questions
Does a setback actually save energy?
For a furnace or a central air conditioner, yes, in the plain sense that the equipment runs less while the house sits at the setback temperature. The Department of Energy's home energy checklist recommends a programmable thermostat for that reason. How much it saves depends on the house, the climate, and how long the setback lasts.
What about a heat pump?
A heat pump gets one temperature, held. ENERGY STAR says heat pumps do not save energy by being turned down when you are away or asleep, because the recovery can bring on the backup heat. Pick a comfortable setting and leave it, and set the mode to heat or cool rather than auto.
Should I buy a smart thermostat?
It helps most in a house that empties on a predictable schedule, or in a household that will never program a thermostat by hand. If someone is home all day and you like a steady temperature, the Building America Solution Center says the savings and comfort gain will be small. Check compatibility with your system before buying.
Why is upstairs so much warmer than downstairs?
Not the thermostat, in most houses. The Building America Solution Center puts large upstairs-and-downstairs differences down to ducts, returns, insulation, air leakage, windows, or shade. A schedule cannot fix a duct leak; sealing the ducts can.
What should you do next?
Set the schedule tonight and do not touch it for a week. In summer, a ceiling fan lets you hold the cooling set point a little higher; which way the fan should turn, and when to switch it off, is the companion to this guide.
