Smart thermostat settings for extreme heat, not just 78°F

Setting the thermostat to 78°F is not bad advice. It is just incomplete advice, especially for California homeowners trying to use smart thermostat settings during an extreme heat wave. A Nest or ecobee is not a wall dial waiting politely for one number. It may enter Eco mode, pre-cool before a schedule change, average a hot hallway with a cooler bedroom, shut the compressor off early, or participate in a demand-response event. During a normal week, those features can be useful. During a heat wave, they can also be the reason the house does something you did not ask for.

The familiar 78°F number keeps showing up because it gives utilities a simple baseline. In June 2026, the Sacramento Bee quoted PG&E saying that each degree above 78°F saves roughly 2% on cooling, and SMUD saying that raising the set point 2°F can save 5–10% on cooling.[1] That is useful as a starting point. It does not tell you whether your thermostat is about to stop cooling because Eco Temperature is set too high, whether a west-facing thermostat is being fooled by direct sun, or whether Smart Recovery is starting the AC before the schedule you thought you had programmed.

There is also the grid side of the advice. Flex Alerts ask customers to conserve during a 4–9 p.m. window, which overlaps the exact part of the day when many California homes are still absorbing heat from the afternoon sun.[2] That context matters, but it should not be confused with device setup. A grid message can ask for conservation. Your thermostat settings decide how that request turns into actual cooling behavior in your house.

Start with the number, then check what can override it

For a plain thermostat, the practical question is mostly: what temperature did you set? For a Nest or ecobee, the better first pass is: what feature is allowed to change, reinterpret, or work around that number?

The order matters. If Eco cooling is set to an aggressive upper limit, changing the regular cool set point from 78°F to 76°F may not help once the thermostat decides the home is away. If Smart Recovery is active, the system may run before the schedule says “cool,” because the thermostat is trying to hit the next comfort temperature on time. If the thermostat sits in afternoon sun, it may be solving a wall problem instead of a room problem.

Nest settings that matter in extreme heat

Nest is where one-line advice breaks down quickly, because the product name hides several different generations. A Nest Learning Thermostat, a Nest Thermostat E, a 4th-gen Nest Learning Thermostat, and the 2020 Nest Thermostat do not all expose the same tools. Before changing anything, identify the model in the app or on the thermostat, because several heat-wave settings are model-limited.

Eco Temperatures: check the cooling range before trusting away mode

Eco Temperature is the first Nest setting I would check before a heat wave. Google says the selectable Eco cooling range is 76–90°F. If “Cool to” is set to Off, cooling will not run in Eco mode unless a Safety Temperature is reached. Google also says presence sensing can take up to 2 hours to switch into Eco after it determines everyone is away.[3]

That means the Eco cooling number is not a side preference. It is the temperature the house may be allowed to drift toward when Nest thinks the home is empty. In mild weather, a high Eco cooling temperature may be harmless. In an inland California heat wave, it can leave the house with too much heat stored in walls, floors, furniture, and upstairs rooms by the time people come home.

For a heat wave, I would rather choose an Eco cooling temperature intentionally than discover it at 5 p.m. after the house has been coasting all afternoon. The right number depends on the house, but the setting should be close enough to prevent a long recovery period if people, pets, or heat-sensitive rooms matter.

Safety Temperatures: do not assume cooling protection is already on

Safety Temperatures are a separate backstop. Google says the cooling Safety Temperature is Off by default for central air, while the heating Safety Temperature is On by default.[4] That default surprises people because “safety” sounds like something the thermostat would already handle in both directions.

Open the thermostat’s temperature preference or safety settings and look specifically for the cooling Safety Temperature. If it is Off, then Eco “Cool to Off” really can mean no cooling in Eco unless another mode or program intervenes. If you turn cooling Safety Temperature on, set it as an emergency ceiling, not as your comfort target. It is the line you do not want the house to cross, not the temperature you want to live at.

Sunblock: useful if the thermostat is in sun, absent on the 2020 Nest Thermostat

A thermostat in direct sun is a small problem that can become a whole-house problem. Google’s Sunblock feature exists on Nest Learning Thermostat and Nest Thermostat E, but not on the Nest Thermostat released in 2020. Sunblock is designed to compensate when sunlight heats the thermostat sensor, so the AC does not overcool the home because the thermostat itself is warmer than the room air.[5]

If your thermostat catches late-afternoon sun, check for Sunblock before assuming the set point is wrong. On supported models, look in Nest Sense or thermostat settings for Sunblock. If you have the 2020 Nest Thermostat, this feature is not available, so the practical fixes move elsewhere: shade the wall if possible, correct the schedule around that heat gain, or use other room readings if your setup supports them. The missing feature matters more than the name on the box.

Airwave: know when the compressor is supposed to stop early

Airwave can make a Nest look as if it stopped cooling too soon, when it is actually using a specific strategy. Google says Airwave shuts off the compressor early and keeps the fan running to use residual cold on the coils for 5–10 minutes. It only activates when indoor humidity is below a Nest-calculated level.[6]

In dry heat, that behavior can be reasonable. In a room that is already lagging behind, it can still be annoying because the loud, expensive part of the system has stopped while you are watching the temperature and waiting for relief. Check Airwave in Nest Sense or thermostat settings. If you turn it off during a heat wave, make that a deliberate temporary choice, then revisit it when conditions return to normal.

Presence sensing and schedules: pre-cooling depends on the Nest generation

Nest’s presence and schedule behavior is another place where model assumptions get people into trouble. Google documents Eco behavior around home and away status, but schedule pre-heating or pre-cooling is identified here for the 4th-gen Nest Learning Thermostat and the 2020 Nest Thermostat, not as a universal feature on every Nest thermostat.[3]

The safest way to use that table is not to treat every row as a feature hunt. It is to stop assuming that another Nest owner’s menu matches yours. If the feature is absent, no amount of better 78°F advice will make it appear.

ecobee settings that change cooling behavior

Ecobee has a different personality. The set point still matters, but the thermostat also leans heavily on schedules, recovery behavior, eco+ adjustments, humidity interpretation, and remote sensors. That can be excellent in a house where the thermostat sits in a bad location. It can also make the system look unpredictable if you only check the main screen.

Smart Recovery: the AC can run before the schedule

Smart Recovery is the ecobee setting to check when the AC starts before a programmed time. Ecobee describes Smart Recovery as pre-heating or pre-cooling in anticipation of a schedule transition, and Stacey on IoT reported ecobee support’s explanation that Smart Recovery can be disabled from the physical thermostat or the web portal, not from the mobile app.[7][8]

I would not turn Smart Recovery off just because it runs before the schedule. During extreme heat, pre-cooling can be exactly what prevents a miserable late-afternoon recovery. The reason to change it is narrower: the thermostat is starting earlier than you want, conflicting with your conservation plan, or cooling rooms that do not need it.

eco+ and humidity adjustment: comfort may be calculated, not just measured

Ecobee’s eco+ features can also affect what the house feels like compared with the number on the screen. Ecobee’s summer-saving guidance points to eco+ Time of Use, Adjust temperature for humidity, and SmartSensor averaging as ways the thermostat can conserve energy or improve comfort during summer conditions.[9]

The humidity feature deserves plain-language attention. If a thermostat adjusts for humidity, it is not simply treating 78°F as 78°F in every condition. It is trying to account for how the air feels. That may be welcome on some days and confusing on others, especially if the displayed temperature and the room comfort do not seem to line up. Before blaming the equipment, check whether humidity-based adjustment is enabled under eco+ or comfort-related settings.

SmartSensors: a hot thermostat wall does not have to speak for the whole house

SmartSensor averaging is ecobee’s practical answer to a common California problem: the thermostat is mounted where the builder put it, not where people actually suffer through the heat. Ecobee’s summer guidance specifically points to SmartSensor averaging for situations where a thermostat may be affected by sun.[9]

During a heat wave, sensor placement is not decorative. Put sensors in the rooms whose comfort you are actually trying to protect, then check which sensors participate in the active comfort setting. A sensor in a cool interior hallway can make the system stop too early for a west-facing bedroom. A sensor in a sun-baked room can make the system run longer than the rest of the house needs. Averaging is only as good as the rooms included in the average.

About ecobee thresholds

Ecobee threshold settings can affect cycling and comfort, but the support pages needed to verify exact threshold language were JavaScript-rendered during research and did not return readable content. That matters because threshold numbers are the sort of detail that gets repeated from snippets and forum posts until it sounds official. This article does not rely on unverified threshold values. If you plan to change compressor differential or staging settings, verify the live ecobee support page or the wording on your own thermostat before treating any specific number as current.

Demand-response programs are a separate override to check

There is one more reason a smart thermostat may not behave like a simple set point: enrollment in a demand-response program. Google’s Nest Rush Hour Rewards documentation describes thermostat behavior during rush hour events, including pre-cooling before an event; Renew Home’s Rush Hour Rewards material also describes rush hour participation as a program that can adjust thermostat operation.[10][11]

That does not mean every unexpected change is a utility event. It means program enrollment belongs on the checklist. If the thermostat changes during the same late-afternoon window when utilities are asking for conservation, look for messages in the thermostat app, email, or utility program dashboard before you start rewriting the whole schedule.

A heat-wave setup path that does not pretend every house is the same

Use 78°F as a starting point if it keeps the house livable. Raise it if the house can tolerate it and you are trying to reduce load. Lower it temporarily if the building needs help recovering before the hottest hours. But do not stop at the number. On a smart thermostat, the settings around the number often decide what actually happens.

1. Set the normal cooling target you can live with. If 78°F works, use it. If a specific room becomes unsafe or unbearable, adjust based on the room, not the slogan.
2. Check away and Eco behavior next. On Nest, review Eco cooling temperature, “Cool to” status, and presence sensing. On ecobee, review eco+ and the active comfort setting.
3. Turn on or verify the safety backstop. On Nest central air, do not assume cooling Safety Temperature is enabled by default.
4. Look for model-limited features before wasting time. Nest Sunblock is not on the 2020 Nest Thermostat. Adaptive Eco is not identified here outside the 4th-gen Nest Learning Thermostat. Some schedule pre-cooling behavior depends on generation.
5. Decide whether early cooling is a problem or a feature. Ecobee Smart Recovery and some Nest schedule behavior can start cooling before the next scheduled period.
6. If the thermostat is in sun, solve the sensor problem. Use Nest Sunblock where available, ecobee SmartSensors where appropriate, or adjust the schedule around the heat gain.
7. Check program enrollment if the thermostat changes during high-demand hours. Rush Hour Rewards and similar programs belong in a separate mental bucket from your everyday schedule.

During extreme heat, the set point is still visible, so it gets blamed first. The quieter settings are the ones worth checking before the next hot afternoon: Eco range, Safety Temperature, Sunblock, Airwave, presence sensing, Smart Recovery, eco+, humidity adjustment, sensor participation, and any demand-response enrollment. If your model lacks one of those features, stop looking for it and work with the controls you actually have.

References

1. CA weather: Does setting your AC to 78 save money, energy, Sacramento Bee, June 2026
2. Save Energy, FlexAlert.org
3. Learn about Eco Temperatures, Eco when away & how to change settings, Google Nest Help
4. Thermostat Safety Temperatures, Google Nest Help
5. Learn about Sunblock and how to change settings, Google Nest Help
6. Learn about Airwave and how to change settings, Google Nest Help
7. Get the most out of your thermostat, ecobee Citizen
8. Why your smart thermostat might run before its programmed times, Stacey on IoT
9. 5 ways to save energy this summer, ecobee Citizen
10. How Nest thermostats work with Rush Hour Rewards, Google Nest Help
11. Learn about Rush Hour Rewards, Renew Home