The Right Way to Set Your Thermostat During a Las Vegas Summer
Every summer, the question comes up: what should the thermostat be set to? You'll find confident advice all over the internet — 78°F when you're home, 85°F when you're away, never lower than 70°F, cool the house down before the heat of the day. Some of it is reasonable. Some of it was written for climates that have nothing in common with Las Vegas. Here's what actually matters in the desert.
The "78°F is ideal" rule is a starting point, not a law
Energy efficiency guidelines often cite 78°F as an ideal summer setting because it represents a reasonable balance between comfort and energy use. That guidance is sensible in moderate climates. In Las Vegas, where the outdoor temperature might be 112°F, the differential between inside and outside is already enormous — your AC is working very hard to maintain 78°F, and going to 72°F requires significantly more energy at those outdoor temperatures.
That said, comfort is real, and heat is genuinely dangerous. The right thermostat setting is the lowest temperature where your household is comfortable and safe, balanced against the cost of maintaining it. There's no universal number, and anyone who tells you otherwise isn't accounting for your home's insulation, sun exposure, or the specific people living in it.
Setback temperature: how much warmer should it be when you're away?
A common recommendation is to raise the thermostat 7–10°F when the house is unoccupied. In Las Vegas summer, there's a limit to how aggressive you should be with that setback. Allowing the house to rise to 88–90°F during a 112°F afternoon means the AC has to pull that temperature back down to 76°F when you return — which can take two hours or more and may actually use more energy than maintaining a moderate setback of 5–6°F.
This is especially true in homes with poor attic insulation or significant west-facing windows. In those houses, the thermal mass heats up significantly during setback periods, and recovering from that heat takes time and energy. A smart thermostat that tracks your schedule and starts cooling the house before you return handles this better than a fixed schedule.
Pre-cooling: does it actually work?
Pre-cooling — running the AC harder in the morning when outdoor temperatures are lower, then letting the house coast through the hottest afternoon hours — can reduce energy costs in some utility rate structures. Las Vegas utility rates vary by time of day (time-of-use pricing), and if your rate plan charges more for electricity during peak afternoon hours, running the AC harder in the morning to build up a "cool bank" in the house's thermal mass can make financial sense.
Whether this works for your home depends on your rate plan, your home's insulation, and how well the house holds temperature. It's worth understanding your NV Energy rate structure before optimizing around it.
Fan mode: "auto" or "on"?
Most thermostats offer two fan settings: auto (the fan runs only when the system is actively cooling or heating) and on (the fan runs continuously regardless). In Las Vegas summer, "auto" is almost always the right choice. Running the fan continuously when the AC isn't actively cooling just circulates warm air from the attic space through the ducts and back into the rooms — particularly in homes with ductwork in unconditioned attic space.
The one exception is homes with very good duct insulation and sealed ductwork, where continuous fan circulation actually helps equalize temperatures between rooms. If you're not sure which category your home falls into, "auto" is the safer default.
What your thermostat can tell you about your system
A thermostat that can't reach its set temperature on a day below 100°F suggests the system is undersized, losing efficiency, or losing cooled air somewhere before it reaches the rooms. A system that cycles on and off very quickly (short cycling) may be oversized, have a refrigerant issue, or have a dirty filter restricting airflow. The thermostat is a useful diagnostic tool — paying attention to how the system behaves relative to outdoor conditions gives you real information about what's happening with the equipment.