How Much Does Setting Your AC to 78 Save?

Published on July 3, 2026 | Written by Alec Pow
This article was researched using 14 sources. See our methodology and corrections policy.

Moving a summer thermostat toward 78 can trim a cooling bill, but the dollar result depends on runtime, local power rates, humidity, and how far the setting moved.

A 78 setting is a usage change first, not a fixed rebate. The bill is still built from kilowatt-hours, the utility rate, peak pricing rules, the AC system, insulation, shade, filter condition, and the hours people are home.

For a U.S. household facing a summer electric bill near $800, a realistic modeled gain can land in the low tens of dollars for the season, with higher savings in hot homes that were using a much colder setpoint.

No purchase is required. The unit context is per summer bill, per kWh, and per thermostat schedule, with the biggest modifiers being occupied hours, away setbacks, and state electricity rates.

TL;DR: Setting the AC near 78 can save about $0 if the home already runs warm, or roughly $63 to $79 on a $792 summer electric baseline when the change produces 8% to 10% lower heating and cooling use.

How Much Does Setting Your AC to 78 Save?

Jump to sections

• Entry A thermostat change itself can cost $0 when the existing thermostat already works.
• Mid DOE says a 7 to 10 degree setback for 8 hours a day can save as much as 10% a year on heating and cooling, based on its thermostat operation guidance.
• All-in DOE and ENERGY STAR point to a 75 to 78 daytime starting point and a 7 degree increase when no one is home in their home cooling tips.
• Hardware ENERGY STAR says certified smart thermostats save about 8% on heating and cooling bills, or about $50 (equivalent to 1.7 hours at $30 per hour, or about $20 in 1990 dollars) a year, in its smart thermostat FAQ.
• Summer bill marker CBS News reported in June 2026 that NEADA estimated Americans would spend nearly $800 on electricity from June through September, up 10.5% from the prior summer, in its summer utility report.

What you’re actually buying

Setting an air conditioner to 78 is a control choice, not a separate product or service. The thermostat tells the cooling system when to start and stop, so the setting affects compressor runtime during occupied hours and how much heat the home holds before cooling starts again.

A manual thermostat can do the job if someone changes it at the right times. A programmable or smart thermostat automates the same habit across workdays, nights, and trips away from home. The substitute is not one single device. It may be a lower setpoint, a fan, window shading, duct repair, filter service, or a newer air conditioner. The difference is that 78 changes operation first. Those other moves change comfort, airflow, heat gain, or equipment performance.

Worked total from a 2026 summer bill

The cleanest way to price the move is to start with a published summer electric bill and apply a published savings band. NEADA projected June to September 2026 residential electric spending to rise from $717 (about $290 in 1990 dollars) in 2025 to about $792 in 2026 in its June price update. TVA EnergyRight cites ENERGY STAR and DOE at 8% to 10% heating and cooling savings from smart thermostat use in its smart thermostat savings guidance.

Using those inputs, $792 times 8% equals $63.36, and $792 times 10% equals $79.20. That brings the modeled summer bill down to $728.64 to $712.80 before taxes, rate tiers, and any comfort devices added back into the home.

Line item	Math used	Result
2026 summer electric baseline	NEADA June to September estimate	$792
Lower modeled savings	$792 x 8%	$63.36
Higher modeled savings	$792 x 10%	$79.20
Modeled remaining bill	$792 minus savings	$712.80 to $728.64

What setting AC to 78 changes

The thermostat setting changes the indoor-outdoor temperature gap. When the indoor target is warmer, heat enters the house more slowly, and the compressor gets more off time. That is why a 78 setting can matter more in a home that was holding 70 to 72 all afternoon than in one that already sits near 76.

It also changes who feels the tradeoff. A person working from home in a sunny room may feel 78 very differently from a household that leaves after breakfast and returns near dinner. The setting works best as part of a schedule, with a higher away setpoint, closed shades, open supply vents, and a clean filter. If 78 leads someone to run a portable AC in a bedroom all day, the central-system savings can shrink or disappear.

The quick dollar math

Per-degree claims need care because they are not a universal bill formula. Angi’s 2026 cooling guide says raising the AC setting between 75 and 78 can save 1% to 3% per degree on energy costs in its AC temperature guide. That is a useful screen, not a promise.

Use the smaller number when the home is well shaded, already warm, or in a milder climate. Use the upper side only when the AC runs long hours and the starting point is low. A change from 72 to 78 is not the same as a change from 76 to 78 because the first move cuts more compressor runtime. The home must still control humidity, and the thermostat should not be pushed so high that the system never runs long enough to dry the air.

Electricity rates

The same saved kWh is worth more in a high-rate state. EIA’s April 2026 residential table lists the U.S. total at 18.83 cents per kWh, California at 35.25 cents per kWh, Arizona at 15.48 cents per kWh, and North Dakota at 12.35 cents per kWh in its April 2026 rate table. The gap matters.

California’s April 2026 residential rate divided by the U.S. total, 35.25 divided by 18.83, equals about 1.87. That means a saved kWh was worth almost 87% more in California than in the U.S. total that month. Time-of-use plans can add another layer because afternoon cooling may fall into a higher-price window. The household with the same thermostat habit can see a different dollar result just by crossing a utility boundary.

AC type and thermostat hardware

Central air, ductless mini-splits, heat pumps, wall units, and window units all react to thermostat settings, but not in the same pattern. A central system may serve the whole house, including unused bedrooms. A room unit cools one zone and can waste less energy if the household only occupies that zone. ENERGY STAR says oversized room air conditioners can cool before they remove enough humidity, and its room AC guidance also warns that poor installation can leak air like a 6-square-inch hole.

Thermostat hardware matters because people forget. A manual thermostat saves money only if someone changes it before leaving, sleeping, or returning. A programmable thermostat holds a fixed schedule. A smart thermostat may learn occupancy, accept app changes, and join utility programs, but the device is not magic. A bad location near a lamp, TV, kitchen wall, or sun patch can make the system run at the wrong time.

After changing the setting

The lowest-cost path is behavioral. Set the thermostat, use shades, keep the fan on auto, and replace filters on schedule. The spending starts when comfort problems expose a separate AC issue. If the system has weak airflow, short cycling, or a dirty outdoor coil, a higher setpoint may not deliver the expected drop because the unit was already wasting runtime.

A homeowner can compare the setting change with maintenance before buying more cooling capacity. A seasonal AC tune-up visit may be the better first step for a neglected central system, and separate AC coil cleaning can matter when dirt blocks heat transfer. If the real issue is one hot room, a wall AC installation is a different buying decision, not a thermostat adjustment.

Hidden costs and comfort tradeoffs

Hidden costs show up when the household compensates for the warmer setting. SRP’s June 2026 summer guide says customers can set 78 to 80 at home and up to 85 away, and it says fan auto mode can save $15 (about $6 in 1990 dollars) to $25 each month compared with leaving the fan on in its Arizona summer tips. If a user leaves the blower on or adds a portable unit, savings can leak away.

Humidity is the other tradeoff. Trane’s 2026 thermostat guide warns that the system still needs enough runtime to remove moisture and says each degree set above 72 can save up to 3% on cooling costs in its 78 degree discussion. A home in humid Florida may need a different comfort plan than a dry Phoenix home, even at the same thermostat number.

Mini cases from different homes

Budget case A renter with a window unit moves from 75 to 78 during the day, closes blinds, and uses a small fan only in the occupied room. The primary driver is zone control. The dollar gain is small, but the risk is also low because no new device is bought and the unit is not cooling empty rooms.

Middle case A detached home with central air was set near 72 all afternoon. Moving the occupied setting toward 78 and raising the away setting during work hours cuts compressor runtime across the whole house. The primary driver is the starting point. This is the kind of home where the 8% to 10% seasonal model can be plausible.

High-use case A hot-state household with long summer runtime and a higher utility bill has more dollars at stake. CBS reported June 2026 state estimates that included Arizona at $1,060, Connecticut at $944, and Washington and North Dakota at $488 in the same state cooling estimates.

The cases do not share the same driver. The renter’s result comes from cooling less space. The central-air home’s result comes from changing a cold starting point. The hot-state home’s result comes from a larger summer bill and more runtime.

Who this cost makes sense for

A 78 setting makes the most sense when the home can stay safe, dry, and livable without a second cooling device. It is a weak move when the system is dirty, oversized, or failing, because the bill may be high for mechanical reasons rather than thermostat behavior.

Direct Energy recommends 78 during the day at home and 82 to 85 away in its seasonal thermostat schedule. SRP gives similar hot-climate advice, with 78 to 80 at home and up to 85 away, in its summer preparation tips. ENERGY STAR describes a smart thermostat as a Wi-Fi device that adjusts heating and cooling settings automatically in its smart thermostat overview.

Makes sense if

• The home sits empty for long workday blocks.
• The current summer setting is much colder than 78.
• The utility rate makes each saved kWh valuable.
• Humidity stays controlled at a warmer setting.

Doesn’t make sense if

• Sleep, health, or humidity needs require a cooler room.
• A portable AC will run to offset the central setting.
• The system has weak airflow, short cycling, or dirty coils.
• The home already uses warm setpoints and long away setbacks.

What we checked

• Checked a utility schedule that places 78 at home and 82 to 85 away in seasonal thermostat schedule.
• Confirmed hot-climate advice with 78 to 80 at home and up to 85 away in summer preparation tips.
• Cross-referenced smart thermostat behavior against ENERGY STAR’s smart thermostat overview.

Article Highlights

• Setting the AC to 78 is a no-purchase move if the thermostat already works.
• The biggest savings come from homes that were set much colder, especially during empty hours.
• A modeled $792 summer bill drops by about $63 to $79 under an 8% to 10% savings band.
• State electricity rates can change the dollar value of the same saved kWh.
• Comfort losses can erase savings if they lead to fan misuse, portable AC use, or deferred maintenance.

Answers to Common Questions

Does setting AC to 78 always save money?

No. It saves only if it reduces compressor runtime or shifts cooling away from higher-use hours. A home already set near 78 may see little change.

Is 78 too warm for sleeping?

It can be. Sleep comfort, humidity, bedding, ceiling fans, and bedroom sun exposure matter. A smaller nighttime setback may work better than forcing one number.

Does a smart thermostat save more than a manual thermostat?

The savings come from the schedule and occupancy response. Smart controls help when people forget, travel, or keep irregular hours.

Should I turn the AC off instead?

For short absences, a higher setpoint is safer than letting the house heat up hard and then forcing a long recovery run. Long absences depend on humidity, pets, and home materials.