How much can heat-advisory smart thermostat settings save?

The irritating thing about asking how much energy smart thermostat settings can save during a heat advisory is that the common answers sound like they are arguing with each other. ENERGY STAR talks about annual runtime reductions and an average bill figure. Google Nest says its thermostats saved about 10% to 12% on heating and 15% on cooling in studies comparing energy bills before and after installation. ecobee has published an “up to 26%” annual heating-and-cooling savings figure against a constant 72°F baseline, plus a 7% to 23% cooling-savings finding for some time-of-use customers in 2020. The familiar DOE-style setback rule is usually repeated as 7°F to 10°F for 8 hours a day to save up to 10% a year. Those numbers do not share a denominator, so they should not be stacked like competing sale prices at the hardware store.[1][2][3][4][5]

This is not another 78°F / 82°F / 85°F setup recipe. If you need the exact heat-advisory schedule and Nest-versus-ecobee menu choices, use NestGrid’s heat-advisory smart thermostat settings guide. The harder question here is what the savings percentages actually measure, and which thermostat move is most likely to cut compressor runtime when the afternoon advisory is real rather than theoretical.

The same thermostat can produce four different savings numbers

A savings claim travels only as far as its method. A percent saved against a constant 72°F house is not the same thing as a percent saved on annual utility bills after installation. A runtime-reduction certification threshold is not the same thing as a demand-response event that trims grid load for a few hot hours. Even the old setback rule is a behavioral rule of thumb, not a brand-specific smart-thermostat result.

The lack of a single accepted evaluation procedure is not a nitpick. Lawrence Berkeley National Laboratory wrote in 2016 that no accepted procedure existed for evaluating connected-thermostat energy savings.[6] That does not make every vendor number useless. It means a defensible number can still be non-comparable.

ENERGY STAR is closer to a program yardstick than a household forecast

ENERGY STAR’s smart-thermostat framing is unusually useful because it talks about runtime, not just dollars. Its FAQ says the specification requires connected thermostats to demonstrate at least an 8% reduction in heating runtime and at least a 10% reduction in cooling runtime. The same FAQ also says certified smart thermostats save an average of about 8% of utility bills, or about $50 per year.[1]

That is a sober number, and it is probably the least flashy one in the pile. But it is not answering, “What will I save if I put my thermostat at 82°F while I am gone from noon to 6 p.m. today?” It is answering a broader program question: across an installed population, does the thermostat reduce annual HVAC runtime enough to qualify, and what average bill effect has ENERGY STAR associated with that category?

That distinction matters in a heat advisory because runtime is the part you can actually influence today. If your air conditioner was going to cycle almost continuously to hold a low setpoint in the late afternoon, a higher setpoint or away setback can remove a visible block of compressor operation. If your house is shaded, well insulated, already set high, or unoccupied with a mild indoor temperature drift, the same nominal setting change may remove much less.

Nest’s 15% cooling claim is a bill comparison, not a per-setting rule

Google’s Nest help page says independent studies found Nest thermostats saved people about 10% to 12% on heating and about 15% on cooling, with estimated average savings of $131 to $145 per year. The method described is a comparison of energy bills before and after thermostat installation.[2]

That kind of pre/post bill comparison is much closer to how a homeowner feels savings: the bill was this much before, then this much after. It also drags in everything that happens around the thermostat. Occupancy patterns change. Weather changes. Someone starts using the upstairs bedroom. A filter gets replaced late. A new rate plan lands. Good studies try to control for these things, but the number is still a broad product-use outcome, not a clean experiment on one heat-advisory setting.

Seasonal Savings belongs in the same mental bucket. ACEEE described Nest Seasonal Savings as adding about 3% to 7% cooling savings by making small schedule adjustments.[7] That is the kind of feature I like when it is transparent: it trims runtime by nudging setpoints and schedules. It becomes a problem when the person in the house does not realize the thermostat has moved the target temperature during the hottest week of the year.

ecobee’s 26% number is high because its baseline is demanding

ecobee’s “up to 26%” annual heating-and-cooling savings figure should not be casually dismissed, but it should be kept in its own lane. The evaluation described that savings against a constant 72°F baseline.[3] A constant 72°F house is a heavy baseline in summer. If your real starting point is already 78°F when home, 82°F when away, and 85°F during a peak-price window, you have already taken much of the low-hanging runtime out of the day.

The same ecobee material reports that Demand Side Analytics found 7% to 23% cooling savings for ecobee users on time-of-use rates in 2020.[3] That is a different and narrower claim. Time-of-use rates reward moving or avoiding usage during expensive hours. A thermostat can look better under that setup if it raises the setpoint during the costly window, uses occupancy sensing aggressively, or precools before the peak period. That does not mean every flat-rate household gets the same percentage.

The setback rule is useful, but it is not a cooling law

The common setback rule says that setting the thermostat back 7°F to 10°F for 8 hours a day can save up to 10% a year. Trane and Reliant both present that DOE-attributed rule in consumer guidance, and Reliant also repeats the rough idea that each degree above 72°F can save about 3% on cooling costs.[4][5] Those are useful reminders that setpoint and duration both matter. They are not permission to turn “one degree equals exactly 3%” into a universal bill calculator.

EnergyHub’s Michigan heating-season analysis is a good warning label. It found about 14 minutes per day of heating runtime per degree, about $10 per month per degree, and about 5.4% per degree in that specific heating-season context, while noting that the DOE 3% per-degree heuristic could understate savings in cold climates.[8] That is not a cooling claim, and it is not a desert-suburb claim. It simply shows why per-degree rules change when the weather, season, fuel, and baseline change.

SMUD’s cooling guidance gives another version of the same caution: it says customers can save 5% to 10% on cooling costs for every two degrees they raise the thermostat, and it also warns that dirty filters can increase energy use by 5% to 10%.[9] The numbers are practical, but they are still rules of thumb. A clogged filter, a duct leak, or a right-sized versus oversized air conditioner can change what a thermostat setting produces on the bill.

During a heat advisory, rank settings by runtime removed

When the compressor is grinding through the afternoon, the cleanest household question is not “Which published percent is right?” It is “Which setting removes the most cooling runtime without creating a comfort or safety problem?” That pushes the thermostat moves into a more useful order.

First: away or eco setback during the hottest occupied-empty hours

The biggest lever is usually the one that changes the most hours. If the house is empty during the late-afternoon peak, away mode, eco temperatures, or a manual temporary hold at a higher setpoint can prevent the system from fighting to maintain a comfort temperature for people who are not there. That is a larger mechanical change than arguing over whether the occupied setting should be 77°F or 78°F.

This is where smart thermostats earn their keep. Occupancy sensing, phone location, schedules, and eco modes can raise the cooling target when the house is empty and start recovery before people return. The savings come from the avoided runtime, not from the leaf icon. If the setback is too small, too short, overridden by comfort settings, or defeated by early recovery, the bill will not care that the feature name sounded efficient.

For actual setpoint examples, use the existing 78°F / 82°F / 85°F heat-advisory setup. The priority here is simpler: set the empty-house temperature high enough to reduce runtime during the peak window, while still protecting pets, people, humidity-sensitive rooms, and any medical needs in the home.

Second: the fixed comfort setpoint

A 78°F occupied cooling setpoint is useful because it gives people a starting point that is not a fantasy low number. But it is a heuristic. Moving from 72°F to 78°F is a very different act from moving from 77°F to 78°F. One changes the system’s work for much of the day; the other may only shave a little runtime at the margin.

The fixed setpoint should come after the away/eco decision because comfort hours and empty-house hours have different consequences. If people are home through the advisory, 78°F may be the tolerable middle. If nobody is home, treating 78°F as a sacred number can waste runtime. If vulnerable people are home, pushing higher just to chase a percentage can be the wrong trade.

Third: Seasonal Savings, eco+, demand response, and precooling

Automation features are worth keeping when they are doing a job you understand. Seasonal Savings can gradually adjust schedules. ecobee eco+ can coordinate features such as smart home/away behavior and time-of-use optimization. Demand-response programs can raise setpoints during grid events. Precooling can move cooling into cheaper or cleaner hours if the rate plan rewards it.

The savings test is the same for all of them: did the feature remove runtime, or did it only move runtime from one hour to another? On a flat rate, shifting runtime may help the grid but not change the bill much. On a time-of-use rate, shifting cooling out of the peak window can matter even if total daily runtime does not fall as dramatically. For rate-plan-specific schedules, use NestGrid’s smart thermostat precooling guide.

Demand response needs its own label. Google says Nest demand-response programs delivered 0.9 kW of per-device peak demand reduction with Consumers Energy in 2020 and 1.06 kW across five utilities from 2020 to 2022.[10] Those are grid-relief figures. They show a thermostat can reduce demand during events. They do not automatically tell one household how much money appeared on the next bill, because the bill effect depends on the program incentive, rate design, event frequency, and what the thermostat did before and after the event.

The line I would draw is consent and visibility. If Seasonal Savings, eco+, or a demand-response event changes the setpoint, the person standing in the hallway should be able to tell what changed and why. If the thermostat seems to be moving itself during a heat wave, NestGrid’s thermostat-changing-settings troubleshooting guide is the better next stop than another savings percentage.

Which number should you trust?

Trust ENERGY STAR when you want a conservative program-level frame for certified smart thermostats. Trust the Nest figure as a broad pre/post bill claim for Nest users, not as a guarantee for one setting. Treat ecobee’s 26% as a high-baseline comparison against constant 72°F, and read its time-of-use findings as evidence that rate plans can make load shifting valuable. Treat the DOE-style setback rule as a directionally useful reminder that larger, longer setbacks save more, not as a personalized forecast.

For a household under an active heat advisory, the first setting to change is usually the away or eco cooling setpoint during empty peak hours. The second is the occupied comfort setpoint. Automation, demand response, and precooling come after that, judged by whether they actually remove runtime or shift it into a cheaper window under your rate plan. If a savings percentage arrives without its baseline, it is not wrong yet. It is incomplete.

That is also why percentages do not transfer cleanly from a manufacturer page to your bill. Climate, insulation, HVAC sizing, utility rates, humidity, occupancy, and starting setpoints decide how much runtime is available to cut. For a fuller look at why a published savings percentage can shrink or grow when it meets real weather and a real rate plan, see NestGrid’s smart thermostat savings and El Niño bill guide.

References

1. Smart Thermostats FAQs for EEPS — ENERGY STAR.
2. Improve energy savings with your Nest thermostat — Google Nest Help.
3. New evaluation report proves ecobee smart thermostats save homeowners up to 26% on annual heating and cooling costs — ecobee, April 2021.
4. Should You Really Set Your Thermostat to 78 in the Summer? — Trane.
5. How to set your thermostat for energy savings — Reliant.
6. Do Connected Thermostats Save Energy? — Lawrence Berkeley National Laboratory, 2016.
7. Smart thermostat initiatives reveal exciting new horizons — ACEEE, 2015.
8. How Much is 1 Degree Worth? — EnergyHub.
9. Heating & Cooling Tips — SMUD.
10. One click away — Google Sustainability.