Pre-cool the house before 3 p.m., raise the setpoint a little when the on-peak window opens, and bring it back down after 7 p.m. That is the whole idea behind running an AC on a TEP time-of-use plan. Climate Pros Tucson explains the schedule here, and matches you with a licensed pro when the equipment or thermostat is the limit.
What hours does TEP count as on-peak?
On TEP’s Time-of-Use plan, the summer on-peak window runs May to September, Monday to Friday, 3 to 7 p.m. In winter, October to April, it runs Monday to Friday, 6 to 9 a.m. and 6 to 9 p.m. TEP also lists Basic, Peak Demand and Demand Time-of-Use plans, so confirm which one is on your bill. Weekends are outside the on-peak window. TEP posts the current hours at tep.com/time-of-use, so check holidays there. If your bill says Trico, not TEP, these hours don’t apply; see Trico Electric customers.
Why does the house feel worst right at 6 p.m.?
The on-peak window covers the late afternoon, when the house has been taking sun all day. At Tucson’s airport the 1991-2020 normal high in July is 100.2F, and the normal low is 76.3F, so the house gets little relief overnight either. If you raise the setpoint at 3 p.m., the indoor temperature climbs slowly through the window, and 6 p.m. is when that drift is easiest to feel. The goal is to bank enough cooling before 3 that the house is still comfortable at 7.
How do you pre-cool before the peak?
Let the AC do its heavy work before 3 p.m. Start the pre-cool in the late morning or early afternoon, and hold the house a little cooler than you normally would. Then you have stored coolness to lean on.
- Close the west-facing blinds before the afternoon sun reaches them.
- Don’t drop the setpoint far below what the system can hold. A system that already struggles on a 100F day won’t catch up.
What does a thermostat schedule look like?
A simple weekday summer schedule has four steps.
- Late morning: cool the house to your comfort point.
- 3 p.m.: raise the setpoint a degree or two so the AC runs less.
- 7 p.m.: return to your normal setpoint.
- Overnight: hold a steady setting rather than swinging it.
A smart or programmable thermostat can run this on its own, and a thermostat installation by a licensed pro is the usual fix if yours can’t hold a schedule. Your own readings will show how far the house drifts. Heavy block walls tend to hold the cool you banked longer, and frame houses tend to drift faster, but your house will tell you. Note the indoor temperature at 3, 5 and 7 p.m. for a few weekdays, and adjust the pre-cool from that. If the house gains more than you can live with, start the pre-cool earlier rather than setting it colder.
What should you avoid running during the peak?
Heat-making appliances add to the AC’s load right when you want it to rest. Run the oven, dryer and dishwasher outside the window where you can. If you’re on one of TEP’s demand plans, read how TEP bills it before you shift big loads; TEP demand time-of-use and your AC covers that plan.
What about a heat pump in winter?
A heat pump heats the house, so the winter on-peak windows matter to you: 6 to 9 a.m. and 6 to 9 p.m. on weekdays, October to April. The same logic applies in reverse, with a pre-warm before 6 a.m. and a slightly lower setpoint during the window. Heat pump mornings on TEP’s winter peak covers the morning schedule and why backup heat strips are the costly part.
Which plan fits your house?
Plan choice depends on when you actually use power. The best TEP rate plan for AC covers how to compare, and why your TEP bill spikes in summer shows where the money goes. For a system that can’t keep up at all, see AC can’t keep up in Tucson heat. The hub at HVAC service in Tucson lists the areas we cover.
When a schedule isn’t enough
Call a pro when the AC can’t hold the house through the on-peak window even after pre-cooling, or when the thermostat can’t run a schedule. Call (520) 353-2520 and we’ll match you with a licensed local pro.