Heatwaves are lasting longer, running hotter, and arriving more often. Air conditioning keeps you safe, yet it can send bills soaring and strain power grids right when everyone needs cooling most. Here’s the good news: with efficient AC use, you can stay cool, protect your health, and save serious energy without sacrificing comfort. Below, you’ll find a guide that breaks down smart thermostat settings, hardware tweaks, and daily habits that work in any climate—so your place stays chill, costs drop, and your footprint lightens.
The real problem in heatwaves: comfort, cost, and capacity
During a heatwave, your AC faces its toughest hours as outdoor temperatures and solar radiation peak. At the same time, neighbors are running their cooling full tilt. Together, those factors create a triple challenge: your unit runs longer to reach the same setpoint, your rate may be higher during peak hours, and local grids can be overloaded. Cranking the thermostat way down to “speed things up” won’t accelerate cooling; the unit will simply run longer and waste energy.
The reason is physics. Heat is moved from indoors to outdoors by AC systems. The larger the temperature difference (for example, 42°C outside vs. 24°C inside), the harder the equipment must work. Humidity adds load, too, because moisture must be removed from the air, and condensation costs energy. In short, heat plus humidity means heavier cooling demand. Indoors, heat sneaks in through windows, walls, doors, electronics, cooking, and lighting. Add those gains together and AC cycles stretch—especially late afternoon, when sun exposure and indoor activity peak.
Globally, cooling has become a major energy user. The International Energy Agency estimates that air conditioning already accounts for roughly 10% of global electricity use and around 20% in buildings—a share that could triple by mid-century without action. Giving up AC isn’t the answer; smarter use is. Set realistic temperatures, reduce heat gains, keep systems tuned, and shift cooling away from the costliest hours when possible. Done well, efficient AC use keeps you comfortable in heatwaves while cutting bills and supporting grid stability.
Bottom line: the issue isn’t needing cooling—it’s running cooling inefficiently during the hottest, most expensive hours. The rest of this guide shows how to flip that script.
Set it smart: thermostat strategies that actually work
Small changes matter. Start with a practical target: many energy agencies suggest about 26–27°C (78–80°F) when you’re home and need cooling, and higher when you’re away or sleeping if that’s comfortable. Consider that a guideline, not a rule—your best setting depends on humidity, insulation, and personal preference. Choose the highest indoor temperature that still feels good. Even a small increase in setpoint shrinks the temperature difference with outdoors, which reduces workload and energy use.
Scheduling helps. Use a programmable or smart thermostat for time-based changes. For example, set 26–27°C when home, 28–30°C when away, and adjust slightly at night if you sleep hot. In very hot regions, pre-cool earlier in the day: bring the home to your comfort level before the afternoon peak, then allow a drift upward by 1–2°C during the most expensive window. If your area has time-of-use rates or heat alerts, automate pre-cooling and reduce demand during peaks to save money and help prevent blackouts.
Two myths are common. First: setting the thermostat lower does not cool the home faster; it just runs the AC longer and can lead to overcooling. Second: “Fan On” isn’t always better; “Auto” is often more efficient because the fan stops with the compressor, limiting moisture re-evaporation. Need a comfort boost? Add a ceiling or pedestal fan. Air movement speeds sweat evaporation and can make you feel 2–4°C cooler at the same temperature, letting you raise the setpoint while staying comfortable. Remember to switch fans off when you leave the room—fans cool people, not spaces.
Humidity matters for comfort. At 26°C, high humidity can feel sticky. Try “Dry” mode if available, or run a dehumidifier to target 40–60% relative humidity. In humid climates, controlling moisture often improves comfort more than chasing a colder temperature. For better sleep on hot nights, pair a slightly higher thermostat with a fan and breathable bedding. Many healthy adults rest well at 24–26°C (75–79°F) with airflow.
Below is a quick-reference table of thermostat actions and their typical impact ranges, based on public guidance.
Action | Typical impact | Source |
Set ~26–27°C (78–80°F) when home; higher when away | Comfortable target that reduces load vs. colder setpoints | |
Raise setpoint 7–10°F (4–6°C) for 8 hours/day | Up to ~10% annual cooling/heating savings | |
Use a ceiling fan with AC | Allows ~2–4°C (≈4°F) higher setpoint with similar comfort | |
Pre-cool before peak hours | Shifts use away from expensive times; supports grid |
Renters or travelers can still apply these tips. Use the highest comfortable setpoint, add a fan, close blinds during the day, and run a portable dehumidifier if humidity is high. Efficient AC use is about strategy, not just hardware.
Upgrade and maintain: hardware tweaks with big impact
Even a smart thermostat plan won’t help if the AC is fighting clogged filters, leaky ducts, or a condenser baking in direct sun. A little maintenance goes a long way—especially under heatwave stress. Start with the filter: check monthly in summer and replace or clean as needed. When filters are dirty, airflow drops, the system runs longer, and evaporator coils may even freeze. Choose a MERV rating your system can handle without too much resistance (when unsure, follow manufacturer guidance).
Coils and airflow come next. Keep the outdoor condenser clear by at least 60–90 cm (2–3 ft) on all sides. Vegetation should be trimmed, debris removed, and shading added if possible without blocking airflow. Rinse outdoor coil fins gently with a hose (pressure washers can damage fins), and keep indoor evaporator coils clean on schedule. If ice buildup is spotted, turn the system off and call a pro—airflow or refrigerant issues may be to blame. Annual checkups can catch low charge, clogged drains, or failing capacitors before the hottest week of the year turns them into emergencies.
With ducted cooling, leaks often waste energy quietly. It’s common for 20–30% of air moving through ducts to be lost via holes, gaps, and poor sealing. Less cold air reaches rooms, so run-time increases. Sealing and insulating ducts—especially in attics, crawl spaces, or garages—can slash waste. Ask for mastic sealing (not just tape) and request test results. If upgrading, consider right-sizing; an oversized unit short-cycles and leaves air clammy, while an undersized one struggles in heatwaves. Variable-speed or inverter systems maintain steady comfort with less energy by matching output to load and improving dehumidification.
Shopping for new equipment? Look for high-efficiency ratings (SEER2/SEER in North America; EER/COP elsewhere) and ENERGY STAR or regional labels. Ductless mini-splits and heat pumps often deliver excellent part-load efficiency and suit zoned cooling or homes without ducts. Smart thermostats can add location-based control, humidity features, and demand-response participation, which may lower bills if your utility offers incentives. In humid climates, pairing cooling with a standalone dehumidifier—or choosing a system with strong latent removal—lets you raise temperature and remain comfortable.
Apartment dwellers using window or portable units can make small upgrades that matter: seal gaps around the unit with foam or panels, keep exhaust ducts short and tidy, and confirm proper drainage. Curtains and reflective films on sun-exposed windows reduce heat entering the space. Those small choices reduce workload and keep rooms comfortable even when outdoor temperatures spike.
For specs, labels, and selection tips, consult authoritative resources like U.S. DOE Energy Saver pages or ENERGY STAR’s product guides before buying.
Daily habits and room setup: free or low-cost wins you can do today
Efficiency isn’t only about the AC; it’s just as much about cutting the cooling your home needs. Sunlight is a big driver. Direct sun through windows can push indoor temperatures up quickly. Close blinds or curtains during the day on sun-facing windows. Reflective shades or light-colored drapes with a white backing reduce heat gains significantly. Exterior shading (awnings, shutters, trees) works even better because it stops heat before it gets inside. At night, in dry climates that cool after sunset, open windows for cross-ventilation to flush out heat, then close them—and the blinds—early in the morning to lock in the cool.
Reduce internal heat sources. Switch to LED bulbs, avoid long oven or stove sessions late afternoon, and run dishwashers and dryers later at night if safe. Unplug electronics or use smart strips to cut “always-on” heat. Keep doors closed to unused rooms unless your system’s return air requires them open; cool the spaces you actually use. If your AC has adjustable vents, send more air to occupied rooms during peak heat.
Humidity again plays a large role. Aim for 40–60% relative humidity for comfort and health. In humid places, run bathroom and kitchen exhaust fans to remove moisture at the source, then shut them off after 15–20 minutes so cooled air isn’t over-vented. If you dry laundry indoors, try doing it when the AC isn’t fighting peak heat, or dry outdoors when possible.
Small spaces can benefit from a simple combo: a fan plus a reasonable thermostat setting. Position fans to move air across your skin—diagonally across the room works well—rather than just stirring hot air at the ceiling. Turn the fan off when you leave. If you use a portable AC, keep the exhaust hose short, insulate it if it passes through hot areas, and seal the window kit to block hot-air leaks.
Evidence backs these quick wins. The U.S. DOE notes that reflective interior shades and draperies can significantly reduce solar heat gain during summer, and exterior shading is even more powerful. Pair shading with raised setpoints and pre-cooling, and run-times and bills tend to drop—while comfort holds steady when it matters most.
Habit or setup change | Why it helps | Typical benefit | Source |
Close blinds/curtains on sunlit windows | Blocks solar gain before it heats rooms | Reflective blinds/drapes can cut gains substantially | |
Cook earlier or use small appliances (microwave, air fryer) | Reduces indoor heat during peak hours | Less cooling load and shorter AC cycles | |
Use fans with AC | Improves perceived cool by increasing airflow | Raise setpoint ~2–4°C with similar comfort | |
Seal gaps around portable/window units | Prevents hot air infiltration | Lower run-time, better temperature stability |
Finally, plan for health and know your limits. During extreme heat, hydrate, take cool showers, and check local guidance. If cooling is lost during a severe heatwave, seek public cooling centers or community resources—health comes first.
Q&A: quick answers to common heatwave cooling questions
Q: Is it cheaper to leave the AC on all day or turn it up when I’m away?
A: It’s usually cheaper to raise the setpoint (or turn the AC off) when you’re away for several hours, then cool back down when you return. Use scheduling or smart thermostats to automate this and consider pre-cooling before peak hours.
Q: What’s the best temperature for sleeping in hot weather?
A: Many people sleep well around 24–26°C (75–79°F) with a fan for airflow. Light bedding, breathable fabrics, and reduced humidity improve comfort without cranking the AC colder.
Q: Do fans actually make rooms cooler?
A: Fans don’t lower air temperature; they help sweat evaporate, making you feel cooler. Use them with AC to raise the thermostat a bit while keeping comfort. Turn fans off when you leave the room.
Q: How often should I change my AC filter in summer?
A: Check monthly during heavy use and replace or clean as needed. Dusty homes, pets, or construction nearby may require more frequent changes.
Q: Should I close vents in empty rooms to save energy?
A: In many ducted systems, closing too many vents increases pressure and can reduce efficiency or even harm the system. It’s usually better to keep vents open and adjust airflow modestly, or use zoning/mini-splits if you need targeted cooling.
Conclusion: cool, calm, and efficient—your heatwave action plan
Heatwaves put pressure on your comfort, your wallet, and the grid. You don’t need heroic measures to beat the heat—just a smart plan. Start by setting a realistic thermostat target (around 26–27°C when home) and scheduling higher temperatures when away. Add airflow with a ceiling or pedestal fan to raise the setpoint without losing comfort, and pre-cool before late-afternoon peaks if your rates spike. Keep your system in fighting shape: clean filters, clear coils, sealed ducts, and good airflow around the outdoor unit. If an upgrade is on the horizon, choose efficient, right-sized equipment with inverter or variable-speed technology and consider a smart thermostat for automation and demand-response benefits. Then layer in daily habits: block sun with blinds or exterior shading, cook earlier or with small appliances, avoid heat-generating electronics during peak hours, and manage humidity to stay comfortable at higher temperatures.
These moves work because they reduce the cooling your home needs and help the AC do its job efficiently. Flexibility is built in: renters, homeowners, and students can all apply them with what they have today. Ready to act? Pick three steps now: raise your setpoint 1–2°C, schedule your thermostat for away times, and clean or replace your filter. Add one habit (close blinds on sun-exposed windows) and one maintenance task (clear space around your condenser). You’ll feel the difference in comfort—and see it on your next bill.
Want to go deeper? Check your utility for time-of-use rates or incentives for smart thermostats and efficient equipment. Explore ENERGY STAR and DOE guides before your next upgrade. Share this plan with friends and neighbors—collective action during heatwaves helps keep communities safe.
In the hottest weeks of the year, smart beats extreme. Use your AC with intention, and you can stay cool, save energy, and support a more resilient grid. Ready to test it out today—what’s one change you’ll make first?
Sources and further reading:
International Energy Agency: Cooling in buildings
U.S. Department of Energy: Thermostats and control systems
U.S. Department of Energy: Room air conditioners
U.S. Department of Energy: Energy-efficient window attachments