Should I Turn Off My AC When I’m Away?
Should I Turn Off My AC When I’m Away?
It’s one of the most common summer questions in Southern California: should you turn off the AC when you leave home? The short answer for most homes and offices is no. Instead, raise the thermostat to a safe setback temperature. This approach cuts energy use, protects indoor air quality, and avoids heat and humidity swings that can harm people, pets, and property.
Quick guidance by scenario
Out for the workday (6–10 hours): Do not turn it off. Set a setback temperature to 80–82°F in summer. If your place holds heat, 78–80°F may be smarter on extreme days.
Weekend away (1–3 days): Set 82–85°F if the home is reasonably tight and shaded. Near the coast or with known humidity issues, keep it closer to 80–82°F for better humidity control.
Vacation (4–14 days): Typically 82–85°F is efficient. In heat waves, consider 80–82°F so the system doesn’t struggle to recover.
Extended absence (2+ weeks): Use 84–86°F if the structure is dry, shaded, and unoccupied. If you store sensitive items (hardwood, musical instruments, wine, electronics), keep closer to 78–82°F and use a smart thermostat for remote checks.
Pets, seniors, or medical needs: Never shut off the AC. Keep a safe range (generally 76–80°F) and monitor remotely.
Why not just switch it off?
Heat buildup costs more later: Letting the space bake means your AC must work harder and longer to pull down temperature and latent heat when you return. That re-cool spike can erase any savings.
Humidity control matters, even in SoCal: Los Angeles County interiors can gain moisture from cooking, showers, plants, crawlspaces, and coastal marine layers. When AC is off, humidity rises, increasing mold and dust mite risk and warping wood floors and cabinets.
Electronics and finishes hate extremes: High attic and room temperatures accelerate component aging, damage finishes, and can compromise stored goods.
Indoor air quality (IAQ): Long off-cycles reduce air filtration. During wildfire smoke events, that’s the opposite of what you want. A smart thermostat can circulate and filter on a schedule without overcooling.
Best thermostat strategies for energy saving while away
Use a smart thermostat: Schedule setbacks, use geofencing, and pre-cool before you arrive. This balances comfort and efficiency.
Aim for modest setbacks: In summer, a 4–7°F increase from your occupied setting is typically optimal. Going too high increases recovery time and humidity risks.
Keep fan on Auto: Constant fan “On” can raise indoor humidity by re-evaporating moisture off the coil when the compressor is off. Auto is usually better for humidity control.
Filter strategy for smoke season: Consider MERV 11–13 if your system allows it without excessive static pressure. Better filtration improves IAQ, but do not exceed system specs.
Address the envelope: Shade, weatherstripping, attic insulation, and window films reduce heat gain so your setback strategy works better.
Heat pumps, inverter AC, and mini-splits
Modern inverter-driven systems (including many mini-splits and variable-speed heat pumps) are exceptionally efficient at holding a steady indoor condition. Rather than switching fully off, they modulate at low power to manage temperature and humidity. That steady, low-load operation is typically more efficient than letting the space overheat and then forcing a rapid, high-power recovery. Our engineering team has manufacturer training from Fujitsu (Japan), Mitsubishi Elektrik (Thailand), Midea (China), Gree (China), and Hier (China), and we see this performance advantage daily in both residential and commercial projects.
Safety, warranties, and insurance requirements
Some issues around "turning it off" intersect with safety and compliance. Rewiring thermostats, bypassing safeties, or opening refrigerant circuits is not a DIY task. Handling refrigerant without proper certification is illegal and dangerous. Many insurance policies, equipment warranties, and local codes require a licensed HVAC professional for system modifications, major repairs, or commissioning. In commercial spaces and multifamily buildings, additional permitting and documentation often apply. If something goes wrong after an unqualified repair, insurers may deny claims.
Special cases to consider
Coastal vs. inland microclimates: Coastal areas experience higher ambient humidity and marine layers; inland zones face intense heat and solar gain. Your ideal setback varies accordingly.
Hardwood, instruments, wine, and art: These are sensitive to humidity swings. Keep a tighter band, use data loggers, and consider a dehumidification strategy.
Server closets and network gear: Provide dedicated cooling or ventilation. Do not rely on whole-home setbacks alone.
Apartments, condos, and HOAs: Rules may restrict thermostat controls, balcony condensers, or filter types. Coordinate before changes.
What about simply opening windows?
Natural ventilation can help on mild days, but in many parts of Southern California it invites wildfire smoke, outdoor pollutants, and moisture-laden marine air. During heat waves, it also adds heat. For short absences, keep windows shut and use a sensible setback temperature.
Local context: service area and background
#1 AC Guys is a fourth-generation family of engineers with 80+ years in engineering experience, focused on healthy air for a healthy life. We specialize in residential and commercial systems, including large and complex projects. Our service area includes Los Angeles County and nearby regions such as Orange County, Ventura County, and Western Riverside County. You will find us working in communities like Los Angeles, Pasadena, Glendale, Santa Monica, Long Beach, Anaheim, Irvine, Santa Ana, Costa Mesa, Newport Beach, Huntington Beach, Ventura, Oxnard, Thousand Oaks, Simi Valley, Riverside, Corona, and more. Our team carries factory training from Fujitsu, Mitsubishi Elektrik, Midea, Gree, and Hier.
Key takeaways
For most absences, do not turn the AC off. Use a setback temperature instead.
Typical summer away settings: 78–82°F for short trips, 82–85°F for longer trips, tighter for coastal humidity or sensitive contents.
Smart thermostats, proper filtration, and envelope upgrades improve both comfort and efficiency.
DIY electrical or refrigerant work is unsafe and can violate insurance and warranty requirements; use a licensed HVAC professional when changes are needed.
Bottom line
Turning the AC completely off often backfires. A thoughtful setback saves energy, protects indoor air quality, reduces mold risk, and keeps your home or business safer for people, pets, and valuables. In Southern California’s varied microclimates, small adjustments and smart controls make a big difference.
Yasmine is currently an Associate Professor of Psychology at Mount Saint Mary College where she teaches a wide array of courses in the Psychology department. She is a Fulbright Scholar spent a year working at the Medical Decision Making Center at Ono Academic College in Israel.
Yet, as many higher education professionals can surely attest to, I have also witnessed the other challenge in group decision making. In academia, engaging in critical dissent is encouraged (reviewed by Jetten & Hornsey, 2014), and while this is a fine attribute, practically,
