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The best thermostat settings for Arizona summer are 78F when home, 85F when away. Setting it lower than 78F forces your AC to run nearly continuously in 115F heat, dramatically increasing your APS/SRP bill. Every degree below 78F adds approximately 6-8% to your cooling costs. The Trane 360 thermostat (included with Trane 18/20 SEER2 systems) maintains +/-0.5F precision automatically.
Best Thermostat Settings for Arizona Summer
78F when home, 85F when away - the Arizona-specific thermostat settings that balance comfort and energy savings. Bradford explains why lower is not always better.
Why 78F Is the Sweet Spot in Arizona
The DOE recommends 78F for cooling when home. In Arizona, this is especially important - your AC is fighting 115F+ outdoor temperatures, meaning every degree lower requires significantly more energy. At 72F, your AC is trying to maintain a 43F temperature differential. At 78F, it's 37F - 14% less work, which translates to roughly 14% lower cooling costs.
The Away Setting: 85F Not 90F
Many homeowners set their thermostat to 90F+ when away to save money. But in Arizona, this can backfire. If your home heats up to 95F+ while you're away, your AC has to work extremely hard to pull it back down to 78F when you return - sometimes running for 2-3 hours straight. 85F is the optimal away setting: it saves energy but doesn't let the house superheat.
Smart Thermostat Settings for Arizona
If you have a smart thermostat (Trane 360, Nest, Ecobee), use these settings: Home: 78F. Away: 85F. Sleep: 76F (slightly cooler for better sleep). Pre-cool: Set to 76F at 4 PM before peak rates (APS/SRP peak is 3-8 PM). Pre-cool before leaving: Drop to 76F 30 minutes before departure, then let it rise to 85F.
APS/SRP Time-of-Use Savings
APS and SRP both offer time-of-use plans where electricity costs 2-3x more from 3-8 PM. Pre-cooling your home to 76F before 3 PM and letting it drift to 80F by 8 PM can save $30-$80/month on your summer bill. Bradford's Trane 360 thermostat handles this automatically.
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