Best Thermostat Setting for Summer Savings

The best summer setting is the highest temperature your household can genuinely live in, with a warmer setback while the house is empty and overnight. If you want a starting schedule, 78°F awake and home, around 85°F while everyone is out, and about 82°F asleep is a defensible one with an actual pedigree. But some households must not do this at all, and that limit is the most important thing on this page.

Where the 78 degrees actually comes from

The number is repeated everywhere and sourced almost nowhere, so it is worth showing you the document. EPA’s ENERGY STAR Program Requirements for Programmable Thermostats, Version 1.1 — a 2005 specification that manufacturers had to meet for a thermostat to carry the label — required partners to ship thermostats with a default schedule. Its Table 2 gives the acceptable setpoint times and temperatures, and the cooling column reads:

Three things follow from seeing it in context. First, 78°F was never presented as a single all-day setting — it was the occupied setpoint in a four-part schedule, and the savings the specification was after came mostly from the 85°F daytime setup, not from the 78. Second, it is twenty years old, and ENERGY STAR no longer certifies programmable thermostats as a product category, so this is a historical specification rather than current consumer guidance. Third, and most usefully: it was an engineering assumption about a typical household’s tolerance, not a finding about your house, your humidity or your family.

Treat it accordingly. It is a good default and a bad rule.

What a degree is actually worth

The rule you will see quoted is that each degree you raise the setpoint saves about three percent of cooling energy. That figure has no citable authority behind it, not DOE’s, not ENERGY STAR’s, and we do not present it as one. What is true is the direction and the reason for it: your air conditioner works against the difference between indoor and outdoor temperature, so raising the setpoint shrinks that gap and cuts runtime. The saving is real. Its size depends on how hot it is outside, how leaky and how well insulated your house is, and where you are starting from — a degree from 72 to 73 is worth more than a degree from 79 to 80, because the gap it removes is a larger share of a smaller gap.

What deserves far more attention than the percentage is what the percentage is a percentage of. EIA’s Residential Energy Consumption Survey put average household spending on air conditioning at about $265 a year nationally — roughly 12 percent of total home energy expenditure — ranging from about $525 a year in the hot, humid Southeast down to roughly $60 a year in the temperate marine region along the West Coast, where nearly half of households did not use air conditioning at all. (RECS 2015 data, published 2018; electricity prices have risen since, so today’s figures are higher, though not by anything like a factor of five.)

So work the arithmetic on your own baseline before you make yourself uncomfortable:

• A ten percent cut to a $265 cooling bill is about $26 a year, or roughly $4.30 a month across a six-month season.
• The same ten percent on a $525 hot-humid-Southeast bill is about $53 a year.
• The same ten percent on the ~$60 mild Pacific coast average is about $6 a year — fifty cents a month.

That last line is the one, and it changes the advice. On the mild coast, a warmer house is buying you almost nothing. Read your climate rather than your state: coastal California barely runs its cooling, while the inland Central Valley — Sacramento, Stockton, Modesto, Fresno — runs it hard through long, hot summers and lands far nearer the national figure than the coastal one. EIA does not publish a Central Valley number and we will not invent one, but the gap between those two Californias is the whole point.

One California-specific factor pushes the other way, though. EIA’s Electric Power Monthly put California residential electricity at 33.25 cents per kWh in May 2026, against a US average of 18.44 cents. Every kilowatt-hour you avoid here is worth roughly eighty percent more than the national average, which is why the section on when you cool, below, matters more in California than the section on how cool you keep it.

The setback myth: does the AC work harder to cool it back down?

No. This is the most durable piece of folk wisdom in home cooling and it is straightforwardly wrong.

Heat flows into your house in proportion to the difference between the outside temperature and the inside temperature. A house sitting at 84°F on a 100°F afternoon is gaining heat more slowly than the same house held at 74°F, because the gap driving that flow is smaller. Over eight empty hours you accumulate a genuine energy saving. When you come home and drop the setpoint, the system does run a long recovery cycle, but it is only replacing the heat that leaked in, and less leaked in than would have if you had held the low setpoint all day. The recovery cannot cost more than the saving, because it is the smaller of the two quantities by construction.

There are three real caveats, and none of them is “it costs more”:

• Comfort during the recovery. The house takes time to come down, and on the hottest days a badly sized or ageing system may struggle to recover at all before evening. If that is happening to you, the problem is capacity, not the setback — see why an AC can’t keep up.
• Humidity re-absorption. In a humid climate, furniture, carpet and drywall reabsorb moisture while the system is idle, and the recovery cycle has to remove it again. This meaningfully erodes the saving in the Southeast. In the dry inland West it is close to irrelevant.
• The heat-pump winter analogue. The one case where setback genuinely backfires is heating, not cooling: a deep overnight setback on a heat pump can trigger electric auxiliary heat strips on recovery, and resistance heat is far more expensive than the compressor cycle it replaced. That is a real effect and it is why heat-pump thermostats have gradual recovery features. It has no summer equivalent — there is no auxiliary cooling.

Setting it for how you actually live

Four periods, four different jobs.

• Awake and home. Start at 78°F, then move it in one-degree steps over a week or two and stop where the household actually objects. Most people find their real limit is a degree or two from where they assumed it was, in one direction or the other. A ceiling fan in an occupied room usually buys you a degree or two of tolerance for very little energy.
• Asleep. Bodies tolerate more heat asleep than awake, up to a point, and the outdoor temperature is falling anyway so the system works less for the same setpoint. Around 82°F is the historical ENERGY STAR figure; whether that is liveable depends a great deal on bedding, ceiling fans and whether your bedrooms are upstairs.
• Away. This is where the money is. Roughly 85°F while the house is empty, per the same schedule. If you have pets, they set the ceiling, not you.
• Vacation. Do not switch cooling off entirely for a long absence in a hot climate. A house left closed in a Valley July can exceed 100°F indoors, which is hard on wood, electronics, musical instruments and anything with an adhesive in it, and it lets humidity and biological growth take hold on a damp evaporator coil. Around 85°F is a sensible floor to leave it at — high enough to save nearly everything the setback can save, low enough to protect the house.

Time-of-use rates change the answer

Most California residential customers are now on a time-of-use plan, where electricity used during the late-afternoon and evening peak window costs materially more than the same electricity used at other times. That turns the question from “how cool” into “when,” and it is the one place where a slightly cooler house can be a cheaper house.

Pre-cooling is the technique: run the system harder in the late morning and early afternoon, before the peak window opens, and let the house coast upward through the expensive hours. You are buying the same cooling at the cheaper price and using the building’s own thermal mass as storage. The setpoint schedule that does this looks backwards — cooler in the early afternoon than in the evening, which is why it never appears on posters.

Two conditions have to hold for it to work. Your house has to hold temperature reasonably well, or it will simply reheat before the peak window ends, and you need to know when your peak window actually is. Look that up on your own utility’s current residential rate page — PG&E, SMUD, SCE and SDG&E all publish them. We deliberately print no rates or window times here, because they change and a stale figure would be worse than none.

This is also the single strongest argument for a programmable or learning thermostat that most reviews never make: the value is not in the app, it is in reliably executing a schedule you would never remember to run by hand. Whether that is worth buying is a separate question with its own arithmetic — see whether a smart thermostat is worth it. This page is about the number, not the device.

Who should not raise the setpoint

Everything above assumes a healthy household that is simply choosing to be warmer. For some people a hot house is not a saving, it is a medical risk, and no amount of money justifies it.

Do not run a warm house to save money if it contains: infants and very young children; adults over 65; people who are pregnant; people with heart, lung or kidney disease, diabetes, obesity or a disability that limits mobility; people taking medications that impair thermoregulation or sweating, which includes many common blood-pressure medications, diuretics, antidepressants, antipsychotics and antihistamines; anyone who has had a heat illness before; and pets, which cannot leave and cannot tell you.

The National Weather Service, drawing on CDC guidance, describes the progression to watch for:

• Heat cramps — painful muscle cramps and spasms, usually in the legs and abdomen, with heavy sweating. This may be the first sign, and it can lead to the other two. Seek medical attention if cramps last longer than an hour.
• Heat exhaustion — heavy sweating; weakness or tiredness; cool, pale, clammy skin; a fast, weak pulse; dizziness, nausea or vomiting; headache; fainting. Move the person somewhere cooler, ideally a well air-conditioned room, loosen clothing, apply cool wet cloths, offer sips of water. Get medical attention if they vomit, or if symptoms worsen or last more than an hour.
• Heat stroke — throbbing headache, confusion, slurred speech, body temperature above 103°F, hot red dry or damp skin, a rapid strong pulse, fainting or loss of consciousness. Call 911 immediately. NWS states plainly that heat stroke is a severe medical emergency and that delay can be fatal. Do not give fluids. Move them somewhere cooler while you wait.

One counterintuitive detail from the same guidance, because it gets this exactly backwards in most household advice: using a fan to blow air at someone may actually make them hotter when heat index temperatures are in the high 90s or above. Above that threshold a fan is moving hot air across skin rather than helping it shed heat.

If your home cannot be kept safe and your cooling has failed or you cannot afford to run it, that is what a public cooling centre is for. Many California counties open them during heat events and publish locations through the county public health department or 211. Using one is not a last resort; it is the intended response.

Fans, blinds and the cheap things that move the number

Three things make a higher setpoint liveable, which is a better route to savings than willpower.

Ceiling fans cool people, not rooms. A fan creates a wind-chill effect on skin; it does not lower air temperature, and running one in an empty room is pure waste. Used in occupied rooms only, a fan generally buys a degree or two of setpoint for a very small fraction of an air conditioner’s power draw. We do not publish an installed price for a ceiling fan, because our cost research has no defensible figure for one — if you get a quote, the break-even is easy to run yourself: divide the installed price by your annual cooling spend and by the fraction you expect to save, and see how many years the answer is.

Blinds and shades on the sun side stop solar gain before it becomes something the air conditioner has to remove, which is always cheaper than removing it afterwards. West-facing glass in the late afternoon is the highest-value target, and it coincides exactly with the peak-rate window.

Shifting heat-producing chores — oven, dryer, dishwasher — out of the hottest hours removes load your cooling would otherwise have to carry, at the most expensive time of day to carry it.

None of these is a thermostat setting, which is why they get one paragraph here rather than a section. If you want the full ranked list of what actually moves a cooling bill and what each item pays back, that is a different page: twelve ways to lower your cooling bill. And if your bill jumped suddenly rather than being merely high, start with why a summer electric bill spikes — a setpoint change will not fix a fault or a rate increase.

FAQ