Is it cheaper to leave the AC on all day in Tucson?

Is it cheaper to leave the AC on all day?

Usually no. A house gains heat faster the bigger the gap between outdoors and indoors, so holding 72 degrees through a 100-degree afternoon fights the largest gap of the day. A modest setback while nobody’s home lets the gap shrink, and that costs less than holding the setting. Tucson adds two wrinkles: warm nights and the TEP peak window. Climate Pros Tucson matches homeowners with licensed pros when the problem turns out to be the equipment, not the setting.

The 1991-2020 normals at Tucson International Airport show about 68 days a year with a high at or above 100F, and a July normal low of 76.3F. The house does not get a long cool night to recover, so a deep setback can leave the system chasing the temperature for a long stretch afterward.

How much of a setback makes sense in Tucson?

A modest one. Raise the setting a few degrees while you’re out, not to the point where the system is off for the day. A big jump forces a long, steady run to catch up, and in July that run can land right on the TEP peak.

If your home has heavy block or adobe walls, they soak up heat all afternoon and give it back in the evening. That can leave a block house warmer inside in the evening than at midday. A moderate setting held steady often feels better than a deep setback in that kind of house. The slump block and adobe cooling guide covers why.

How does TEP’s time-of-use plan change the answer?

If you’re on TEP’s Time-of-Use plan, the summer on-peak window runs May to September, Monday to Friday, 3 to 7 p.m., as listed on TEP’s time-of-use page. TEP also lists Basic, Peak Demand and Demand TOU plans as alternatives. Your plan name and its exact hours are on your bill and on TEP’s site, so check them before you build a schedule around them.

That flips the setback question on weekdays. A setback that ends at 4 p.m. puts the long catch-up run inside the expensive window, so on a time-of-use plan you end the setback before 3 p.m. instead, then let the setting drift up a little through the peak. The hour-by-hour version is in the TEP time-of-use AC schedule.

What about a vacant house or pets?

For a house that’s empty for days, set the thermostat higher than normal but leave cooling on. With the cooling off through a run of 100F days, nothing stops the inside from climbing. Snowbirds leaving for the summer have more to plan; see summer AC for a snowbird home. If a pet stays home, don’t use the vacant-house setting. Ask your vet what’s safe for your animal.

Older adults at home are a separate case. The CDC advises older adults to stay in air-conditioned buildings in hot weather and not to rely on a fan as the main cooling when it’s very hot. Don’t push a setback for the sake of the bill.

Does a smart thermostat settle it?

It helps with consistency, not with physics. A schedule that pre-cools before the peak and relaxes through it is easy to run once and forget. Our smart thermostat guide covers the setup. If the system can’t hold temperature even on a steady setting, the cause is usually sizing, ducts or a failing part, not the schedule. See why an AC can’t keep up in Tucson heat.

When the setting isn’t the problem

If your system runs all afternoon and the house still won’t cool, a licensed pro should check charge, airflow and sizing. Start with AC repair or the Tucson hub. Call (520) 353-2520 and we’ll match you with a licensed local pro.