Does Smart Thermostat Pre-Cooling Work in a Heat Advisory?

Investigated/Reference status: checked on 2026-08-25. NestGrid did not reproduce these thermostat settings in a test home; this is a source-checked operating recipe built from utility, manufacturer, and program guidance.

Pre-cooling sounds simple until the utilities start disagreeing with each other. In NPR’s July 2025 reporting on “supercooling” and pre-cooling, Arizona Public Service promoted cooling the house earlier in the day and raising the setting during its 4–7 p.m. peak window, Georgia Power said pre-cooling only works in an extremely efficient home, and Exelon warned that very low settings can raise costs and strain air-conditioning equipment. Researchers in the same reporting cautioned against extreme supercooling and rapid on/off cycling rather than treating the tactic as a universal heat-wave fix. [1]

That split matters for anyone searching for smart thermostat settings for a heat advisory and trying to stay cool without turning the schedule into folklore. Pre-cooling can be a good move when the bill has a peak-price problem and the house can hold the cooler air. It can also be pointless, expensive, or uncomfortable when the rate plan is flat, the building leaks heat fast, or the thermostat is driven far below a normal occupied setting.

The most defensible copyable schedule

Tucson Electric Power gives the cleanest source-backed pattern in the available material. For customers on its summer weekday on-peak window, TEP says to pre-cool for the three hours before the 3–7 p.m. peak period from May through September. Its example starts with a normal occupied setpoint of 78°F, lowers the thermostat to 75°F from noon to 3 p.m., then raises it to about 81°F during the 3–7 p.m. on-peak window. [2]

The important part is not the number 75 by itself. The important part is the modest three-degree drop before a specific peak window, followed by a modest raise during that window. That is very different from driving the thermostat far below normal in the morning and hoping the house behaves like a freezer pack through a heat advisory.

If your utility’s peak period is not 3–7 p.m., do not copy TEP’s clock times blindly. Copy the shape only when your rate plan gives you a real reason: normal setting, then a small pre-peak drop, then a higher setting during the expensive period. If your normal setting is not 78°F, avoid turning this into an arithmetic dare. The source-backed example supports a modest pre-cool, not an extreme “as low as the system will go” routine.

When pre-cooling has a real reason to work

No single source in this evidence set gives a complete universal rule for every house, rate, and heat advisory. The usable rule is NestGrid’s synthesis across TEP’s time-of-use schedule, Georgia Power’s caveat about extremely efficient homes, SEPA’s demand-response framing, and the researcher cautions reported by NPR: pre-cooling is worth trying only when four conditions line up. [1][2][3]

• Your rate plan has a peak-price or demand-charge reason. Without a time-of-use, critical-peak, or demand component, shifting compressor runtime earlier may not save money. It may simply run the air conditioner longer.
• The house can hold the cooler air. Georgia Power’s warning is the quiet dealbreaker: if the home gains heat quickly, a noon pre-cool may be gone by late afternoon. [1]
• The temperature delta stays modest. TEP’s example uses a three-degree pre-cool and roughly a three-degree peak raise around a 78°F normal setting. [2]
• The system is not being forced into harsh recovery. Exelon’s warning about very low settings raising costs and straining equipment is the line between controlled pre-cooling and punishing the compressor. [1]
• The people in the home can tolerate the peak-period setting. A heat advisory is not the time to let an automation goal outrank a vulnerable occupant, a medical need, or a room that runs hotter than the thermostat location.

Those conditions also explain why flat advice fails. “Set it lower before peak” is not physics by itself; it is a billing-and-building strategy. The billing part decides whether moving cooling earlier has value. The building part decides whether the house keeps enough of that cooling to make the later raise tolerable.

For broader heat-wave starting points that are not specifically about pre-cooling, NestGrid’s copyable thermostat settings for a heatwave and smart thermostat heat-dome settings cover normal occupied, away, sleep, and safety setpoints. This article is narrower: whether to deliberately cool early before a peak window.

How ecobee and Nest fit into the same pattern

ecobee’s utility-facing features are an implementation path for the same basic shape: cool before the event, reduce cooling during the peak, and let the occupant override if needed. ecobee says Community Energy Savings may pre-cool the home before an energy event, make small temperature adjustments during the event, offer one-touch opt-out, and provide up to $125 in rewards depending on the local program. Its eco+ Time of Use feature also describes pre-cooling or pre-heating when energy is cheaper, then reducing HVAC use when electricity is more expensive. [4]

That does not make every ecobee adjustment a utility demand-response event, and it does not mean every unexpected schedule change is pre-cooling. If your thermostat appears to change itself during a heat wave, the overlap between eco+, utility events, and comfort schedules is better handled in NestGrid’s troubleshooting guide to why your thermostat changes its own settings in a heat wave.

Google Nest support material describes a different but related behavior: a Nest thermostat may start cooling early so the home reaches a scheduled temperature on time, including when the home is away, and then return to Eco Temperatures after reaching that scheduled temperature. That is schedule optimization, not proof that pre-cooling will lower your bill under a flat rate. [5]

The reason smart thermostats are better suited to this than old-school air-conditioning cycling is control. SEPA describes modern smart-thermostat programs as moving beyond blunt 15-minute AC cycling toward approaches that use temperature ceilings, pre-cooling, and one-touch override. That distinction is practical during a heat advisory: the homeowner is not supposed to be trapped inside an invisible utility command. [3]

What to expect from savings claims

The most useful savings baseline here is not a dramatic vendor percentage. ENERGY STAR says certified smart thermostats save users an average of about 8% on heating and cooling bills, or about $50 per year, and certified models must support utility demand-response functionality. That is a calibration point, not a promise that one afternoon pre-cool schedule will be visible on the next bill. [6]

ecobee’s “up to 23% more cooling savings” claim for eco+ Time of Use is explicitly tied to a vendor-commissioned summer 2020 study, so it should be read as a bounded claim about that program and study design, not as an independent guarantee for every house in a heat advisory. The same caution applies to larger annual comparisons framed against a constant 72°F hold: that baseline is colder than many households’ normal cooling setting, so the result is not the same question as “will a modest pre-cool help my 78°F house ride through a 3–7 p.m. peak window?” [4]

For a deeper look at ecobee savings math, see NestGrid’s ecobee smart thermostat savings verification. The short version for pre-cooling is simple enough: a smart thermostat can automate a sensible rate strategy, but it cannot make a leaky envelope, oversized delta, or flat rate plan behave like a peak-pricing success story.

When to skip pre-cooling during a heat advisory

Skip the pre-cool experiment if the house is already struggling to stay at its normal safe setpoint. A thermostat cannot bank comfort that the building immediately loses, and a heat advisory raises the consequence of being wrong. In that case, use the cooling setting that keeps the occupied rooms safe and tolerable rather than asking the compressor to chase a low noon target and then recover from an uncomfortable peak-period raise.

• Skip it on a flat electric rate unless you have a separate comfort reason to cool earlier.
• Skip it in a poorly insulated or very leaky home where the indoor temperature rebounds quickly.
• Skip aggressive drops that push the air conditioner into long, hard runs or rapid cycling.
• Skip peak-period raises that make bedrooms, upstairs rooms, nurseries, work rooms, or medically sensitive spaces unsafe.
• Skip it if you do not know whether your thermostat’s change came from your schedule, a utility event, occupancy sensing, Eco mode, or an energy-saving feature.

If the conditions do line up, the TEP-style pattern is the version worth trying first: keep your normal safe occupied setpoint, pre-cool by a few degrees before the actual on-peak window, then raise a few degrees during that window and keep override available. If those conditions do not line up, the better smart thermostat setting during a heat advisory is your normal safe cooling setpoint, not an aggressive pre-cool experiment.

References

1. Heat is testing a controversial hack to save on AC bills. Does 'supercooling' work?, NPR, July 23, 2025
2. Pre-Cooling Your Home in the Summer, Tucson Electric Power
3. Smart Thermostats Bring New Life and Innovation to AC Cycling, Smart Electric Power Alliance
4. eco+ Community Energy Savings, ecobee
5. Learn about Eco Temperatures and how to change settings, Google Nest Help
6. Smart Thermostat FAQ, ENERGY STAR