How to Set Your Smart Thermostat for a Heatwave

The first sign that your smart thermostat needs a heatwave override is usually not a warning message. It is the app proudly showing an energy-saving mode while the hallway is hot, the AC has been running for hours, and the house still has not recovered from an aggressive afternoon setback.

For heatwave days, stop letting the thermostat make big decisions on your behalf. Use a flatter cooling plan, keep the blower from running continuously, precool only when it makes sense for your rate plan, and temporarily tame learning, recovery, geofencing, and demand-response features that create large temperature swings.

Use this heatwave profile first

These are starting settings, not comfort commandments. A commonly used summer baseline is 78°F when home, 85°F when away, and 82°F for sleep, but heat-sensitive people, upper-floor bedrooms, poor insulation, and oversized west-facing windows can all justify a cooler number.[1] If anyone in the home is medically vulnerable, treat comfort as a safety issue and use NestGrid’s companion guide, Smart Thermostat Heatwave Settings That Prevent Heatstroke, instead of optimizing mainly for energy.

The fan setting deserves immediate attention. In cooling mode, a wet evaporator coil is part of normal AC operation. When the fan runs continuously after the compressor shuts off, it can blow some of that moisture back into the home, raising indoor humidity and making the same temperature feel worse.[2] During a heatwave, “fan ON” often sounds like extra cooling. It is usually just extra air movement over damp equipment.

Precooling is the one planned exception to the flat-schedule rule. SMUD advises customers to cool homes earlier in the day and use 78°F during peak periods, while Tucson Electric Power gives a concrete example of setting the thermostat 3°F lower for 3 hours before on-peak hours.[3][4] That does not mean every home should overcool aggressively; it means that if your utility charges more in late afternoon, a small, scheduled head start is better than letting the thermostat discover at 5 p.m. that the house is losing.

Nest heatwave settings

Nest’s best features are not bad features. Auto-Schedule, Eco Temperatures, Home/Away behavior, and Airwave can be elegant in normal summer weather. In a heatwave, the job is narrower: stop the thermostat from creating a setback that your AC cannot comfortably erase.

1. Put Nest in Cool and use a temporary Hold

Open the Nest app or Google Home app, choose your thermostat, and set the mode to Cool. Pick your heatwave home temperature, often 76–78°F for healthy households that can tolerate it, then use Hold if your model and app interface support it. If Hold is not available in the place you expect, flatten the schedule manually for the next few days instead of letting the normal weekday pattern run.

The point is not to make Nest dumb forever. The point is to stop a learned schedule from letting the house drift high in the afternoon and then asking the AC to claw back several degrees when outdoor heat is at its worst.

2. Turn Auto-Schedule off temporarily if it keeps rebuilding deep setbacks

On Nest Learning Thermostat models, look for Auto-Schedule in the thermostat or app settings and turn it off during the heatwave if it keeps adding warmer periods you do not want. Then inspect the cooling schedule and remove large afternoon gaps. A simple heatwave schedule can be as plain as:

• Morning: normal home cooling setpoint
• Pre-peak period, if you have time-of-use rates: 2–3°F cooler for a limited window
• Peak afternoon: steady home setpoint, not a large setback
• Night: sleep setpoint adjusted for the hottest bedroom, not the coolest hallway

3. Set Eco Temperatures so “away” does not become a recovery trap

Nest Eco Temperatures let the thermostat use an energy-saving temperature when the home is unoccupied or manually placed into Eco. For a heatwave, set the cooling Eco Temperature near your real away target—often around 85°F if your home setting is around 78°F—instead of letting away mode climb so high that the home cannot recover before evening.[5]

If your house gains heat quickly, 85°F may still be too warm. Use the smallest setback that actually saves runtime without turning the return-home period into a two-hour compressor marathon.

4. Leave Airwave on unless comfort tells you otherwise

Nest Airwave can turn off the compressor while continuing to run the fan briefly, using residual cooling from the coil. Google says Airwave is automatically suppressed when indoor humidity is above Nest’s calculated threshold, which is exactly the kind of guardrail you want during muggy heat.[6]

So the default heatwave recipe is Airwave ON, fan schedule OFF or minimal, and system fan behavior left on AUTO. If the house feels clammy, watch indoor humidity and comfort rather than assuming the lower runtime number is the whole story.

5. Check Home/Away behavior before you blame the AC

If people are home during the day, make sure Nest is not switching into Eco because phone location, occupancy sensing, or a quiet room makes the home look empty. During a heatwave, a false away event is not a small optimization. It is the thermostat deliberately raising the target while the building is already under stress.

ecobee heatwave settings

With ecobee, the heatwave work is mostly about eco+, humidity, fan runtime, and occupancy behavior. Exact menu wording can vary by model, app version, and account setup, so treat the paths below as practical locations to look rather than a promise that every screen will be named identically.

1. Flatten your Comfort Settings and schedule

Open the ecobee app, go to your thermostat, and review Comfort Settings such as Home, Away, and Sleep. For heatwave days, keep Home in the range your household can actually tolerate, set Away only moderately warmer, and avoid a big afternoon jump. Then open the schedule and remove long hot blocks that force the system to recover right before dinner.

A good ecobee heatwave schedule is boring: Home or a similar custom comfort setting for most occupied hours, a small precool block before peak pricing if you use time-of-use rates, and a sleep setting that reflects the warmest bedroom.

2. Keep eco+ humidity help, but do not let savings logic overrule comfort

ecobee describes eco+ as a set of features that can adjust operation for time-of-use rates, humidity, occupancy, and energy events. Its Time of Use feature can precool during off-peak periods, and ecobee attributes 7–26% additional cooling-cost savings to eco+, depending on conditions and setup.[7] That is useful, but it is still an estimate from the vendor, not a guarantee for your house.

For a heatwave, keep Adjust for Humidity enabled. That feature is designed to account for how humidity changes perceived comfort, which matters more on a 96°F sticky afternoon than it does on a mild shoulder-season day.[7] If eco+ has a savings slider or preference level in your app, choose a less aggressive setting while the heatwave is active.

3. Verify Smart Home & Away before it quietly changes the plan

Smart Home & Away can be helpful when occupancy is predictable. During extreme heat, check that it is not putting the house into Away while someone is working upstairs, napping, or sitting outside the sensor’s usual activity zone. If the thermostat keeps misreading occupancy, disable that behavior temporarily or use a manual hold.

4. Set fan minimum runtime to 0 or low

In ecobee settings, look for the HVAC or system fan controls and find Fan Minimum Runtime. During a humid heatwave, set it to 0 minutes per hour or another low value unless you have a specific circulation problem you are solving. The AC should dehumidify while cooling; the fan should not spend the rest of the hour re-evaporating moisture and mixing it through the house.

5. Disable Smart Recovery if it pulls cooling into the wrong hours

If your ecobee begins cooling much earlier than expected so it can hit a scheduled setpoint exactly, Smart Recovery or a similar recovery feature may be involved. In normal weather, that can make the house feel seamless. In a heatwave with peak pricing, it may start the compressor early and still leave you paying for cooling during the least convenient hours. If you see that pattern, turn Smart Recovery off for cooling until the heat breaks, or flatten the schedule enough that there is little recovery for it to manage.

6. Know how to opt out of Community Energy Savings events

If your ecobee participates in Community Energy Savings or another utility event program, learn the opt-out control before the hottest afternoon arrives. Demand-response events can be reasonable when the house has been prepared. They are much less reasonable when an upstairs bedroom is already uncomfortable or someone at home cannot tolerate a warmer indoor temperature.

Generic smart thermostat settings that work across brands

If your thermostat is not Nest or ecobee, the labels change but the pattern survives. Look for any setting that learns schedules, starts recovery early, uses geofencing, changes setpoints for utility events, or runs the fan for circulation. Those are the places where normal smart behavior can become heatwave friction.

A copyable generic schedule might look like this: 77°F from morning through early afternoon, 74–75°F for a short pre-peak window if electricity is cheaper then, 78°F through peak pricing, and 79–82°F overnight depending on bedroom comfort. If your home cannot hold 78°F in late afternoon, do not keep lowering the setting to 72°F and expecting a different machine to appear. Set a realistic target, reduce heat gain, and keep the system from losing ground earlier in the day.

Why smart thermostat logic can backfire in extreme heat

The familiar efficiency advice—raise the setpoint when away, let the thermostat learn, let recovery handle the timing—assumes the AC has enough capacity and time to recover. During a heatwave, that assumption can fail. HVAC guidance on heatwave thermostat behavior commonly points to the same problem: deep setbacks and automatic recovery can leave equipment trying to catch up during the hottest part of the day, while geofencing can create repeated swings when people come and go.[8][9]

That is why the heatwave recipe looks flatter than a normal energy-saving schedule. The AC often performs better when it maintains a moderate indoor temperature than when it allows the house, furniture, walls, and upstairs rooms to absorb heat for hours and then tries to reverse all of that heat gain at once.

Savings estimates are still useful as guardrails. Trane cites a rough estimate of about 3% cooling-energy savings for each degree the thermostat is raised above 72°F, while SMUD gives an estimate of 5–10% savings for every 2°F increase.[10][3] Those numbers vary with climate, insulation, equipment condition, humidity, and rate plan. They should encourage moderate setpoints, not trick you into choosing a setback your home cannot recover from.

Small cooling moves that help the thermostat plan

Keep the non-thermostat list short: close blinds before direct sun hits the glass, use ceiling fans only in occupied rooms, avoid adding oven and dryer heat during peak afternoon hours, and drink water before you feel overheated. These steps reduce the load your thermostat is trying to manage; they do not replace a sane cooling schedule.

Ceiling fans are different from the HVAC blower. A ceiling fan can make people feel cooler through air movement, but it does not lower room temperature. Turn it off when the room is empty. The thermostat fan, by contrast, moves air through the HVAC system and can worsen humidity if it runs continuously after cooling cycles.

Optional advanced pattern: Home Assistant heatwave profile

For Home Assistant users, the useful pattern is a temporary heatwave preset triggered by outdoor temperature and utility rate period. Treat the following as a template idea for a generic climate entity, not a hub-tested configuration. Verify entity names, HVAC modes, safety limits, and your thermostat integration before using it.

alias: Heatwave thermostat profile
mode: single
trigger:
  - platform: numeric_state
    entity_id: sensor.outdoor_temperature
    above: 95
condition:
  - condition: state
    entity_id: input_boolean.heatwave_profile
    state: "on"
action:
  - choose:
      - conditions:
          - condition: state
            entity_id: binary_sensor.utility_peak_period
            state: "off"
        sequence:
          - service: climate.set_temperature
            target:
              entity_id: climate.downstairs
            data:
              hvac_mode: cool
              temperature: 75
      - conditions:
          - condition: state
            entity_id: binary_sensor.utility_peak_period
            state: "on"
        sequence:
          - service: climate.set_temperature
            target:
              entity_id: climate.downstairs
            data:
              hvac_mode: cool
              temperature: 78

If you build a version of this, add guardrails: do not run it for medically vulnerable occupants without a safer comfort ceiling, do not let it fight manual changes, and do not assume one downstairs thermostat protects upstairs bedrooms. Utility-rate-aware precooling can shift demand: one 2026 study abstract reported more than 50% peak-load shifting and 28.7–51.3% cost reductions in its evaluated precooling cases, but that finding is scoped to the study conditions described in the abstract, not a promise for every home.[11]

After the heatwave, undo the temporary overrides

When outdoor temperatures return to normal, remove the heatwave hold, restore your usual schedule, and re-enable the smart features you actually like: Nest Auto-Schedule, ecobee eco+ preferences, Smart Recovery, geofencing, or utility programs that make sense in ordinary weather. Leave behind only the lessons that proved true in your house, such as a lower fan runtime, a smaller away setback, or a more realistic upstairs sleep setting.

During extreme heat, smart behavior is useful only when it is constrained by a flatter, less dramatic, humidity-aware cooling plan. If the household is healthy, that plan can still save energy. If someone is medically vulnerable, use the heat-safety settings first and optimize later.

References

1. Smart Thermostat FAQ, ENERGY STAR
2. This One Thermostat Setting Can Make You Sweaty in Summer, Coolray
3. Heating and Cooling, SMUD
4. Pre-Cooling Your Home in the Summer, Tucson Electric Power
5. Learn about Eco Temperatures, Eco when away & how to change settings, Google Nest Help
6. Learn about Airwave and how to change settings, Google Nest Help
7. eco+, ecobee
8. Why Smart Thermostat Settings Can Backfire During Heat Waves, Meyer-Depew
9. Setting Your Thermostat: Tips for Extreme Heat, Luxury Heating, 2025
10. Should You Really Set Your Thermostat to 78 in the Summer?, Trane
11. ScienceDirect article abstract, ScienceDirect