What Is Supercooling — and Does It Actually Work in Phoenix?
Supercooling is the Phoenix time-of-use strategy of running your AC hard during cheap off-peak hours — driving the house several degrees colder than you normally would — then letting it coast through the expensive peak window with the system barely running. It works because your house is a thermal battery: walls, floors, and furniture store 'cold' (really, absorbed heat capacity) and give it back slowly. Done on the right rate plan, in a reasonably tight house, it cuts real dollars off summer bills without cutting comfort. Done on the wrong plan or in a leaky house, it's theater. Here's the honest playbook.
How does supercooling actually work?
Your house weighs tens of thousands of pounds, and every pound of it stores heat. When you hold the thermostat at 71° for hours, you're not just cooling air — you're pulling heat out of drywall, tile, concrete, and furniture. That stored capacity is the battery. When the AC then stands down for the peak window, the mass re-absorbs heat slowly, and the air temperature drifts up over hours instead of minutes.
Time-of-use rates are the other half of the machine. Phoenix's utilities price the same kilowatt-hour wildly differently by the clock — cheap when solar floods the grid at mid-day, expensive when the whole Valley comes home and every compressor kicks on at once. Supercooling simply buys cooling when it's cheap and spends the stored cold when it's expensive. No gadget required — though a smart thermostat runs the schedule better than a human ever will.
There's an equipment bonus, too: the system does its heavy running in the cooler part of the day, when the condenser rejects heat into 95–105° air instead of 115° air — lower head pressure, easier duty per hour of work. Your AC's hardest possible assignment is flat-out running at 5 p.m. in late July; supercooling is partly a scheme to never ask for it.
Plan Fit
The strategy is rate arbitrage — the plan decides the schedule and whether there's anything to win. Windows verified against APS and SRP published plans, July 2026.
Which rate plans does supercooling work on?
SRP Conserve 6–9 p.m. and Save
Cheapest hours 8 a.m.–3 p.m. · peak 6–9 p.m.The purpose-built supercooling plan. Mid-day super off-peak energy is the cheapest SRP sells — in July and August, SRP's published rates put on-peak energy at roughly six times the super off-peak price. Cool hard through the 8-to-3 window, hold through the late afternoon, coast 6–9 p.m., resume after 9.
SRP Manage Demand 5–10 p.m. and Save
Lower prices all day + demand charge measured 5–10 p.m.Here supercooling attacks the demand charge: your bill's demand line is set by your single highest usage hour between 5 and 10 p.m., and the AC compressor is the biggest load in the house. Pre-cool before 5, stagger the oven and dryer, and the month's demand peak shrinks with the AC's evening runtime.
SRP Time-of-Use (legacy, 2–8 p.m. peak)
On-peak 2–8 p.m. weekdays, May–Oct — closed to new enrollmentThe plan that made supercooling a Valley folk art: six expensive afternoon hours, so households learned to bank cold all morning. Existing customers can stay on it until the November 2029 billing cycle — if that's you, your pre-cool deadline is 2 p.m., the earliest in the Valley.
APS Time-of-Use 4pm–7pm Weekdays
On-peak 4–7 p.m. weekdays, year-roundOnly three hours to beat — the friendliest peak window for supercooling. Pre-cool through the early afternoon, let the house ride 4–7 p.m., and weekends don't even have a peak. The demand-charge variant adds the same appliance-staggering logic as SRP's demand plan; the frozen Saver Choice Plus plan keeps a 3–8 p.m. window.
Flat plans (SRP Basic, M-Power, APS flat options)
Same price all hoursThe honest answer: supercooling saves you nothing here — there's no cheap hour to buy and no expensive hour to dodge. If your household can't shift usage, a flat plan can beat a badly-played time plan; if you CAN shift, the time plans plus supercooling are where the money is.
Full utility pictures — territory, every live rebate, plan lineups — APS customers · SRP customers
The Playbook
Same physics on every plan — only the clock changes.
The four-step supercooling routine
Confirm your plan and peak window first
Supercooling is rate arbitrage — it only pays against a time-based plan. Check which plan your APS or SRP account is actually on (the bill says), because the strategy's whole schedule hangs on your peak window: 2–8, 4–7, 5–10, or 6–9 p.m. are all different games.
Bank the cold during your cheapest hours
Set the thermostat 3–5° lower than your normal comfort temperature through the off-peak or super off-peak window — many Valley supercoolers run the house at 70–72° while energy is cheap. You're not chilling air; you're chilling drywall, tile, and furniture. Mass is the battery.
Step up, don't jump, into the peak window
When peak begins, raise the setpoint above your comfort temperature — 78–82° is the common band — so the AC holds off while the banked cold carries the house. A gradual two-step (comfort temp an hour before peak, then the high hold) beats one big jump and keeps the system from fighting itself.
Resume normal after peak — and automate all of it
After the window closes, return to your normal setpoint. A smart thermostat runs this schedule perfectly every weekday without anyone touching it — and both utilities pay you to enroll one in their thermostat programs (credits below).
Honest Limits
We'd rather tell you before your first bill does.
Where supercooling disappoints
A leaky house drains the battery
Supercooling lives or dies on how long your house holds the banked cold. Thin attic insulation, leaky ducts, and gappy weatherstripping bleed it out in an hour, and the AC ends up running during peak anyway — the strategy's worst case. If your house can't coast, fix the envelope first: that's exactly what the efficiency evaluation measures.
It shifts cost, not kilowatt-hours
Total energy use usually stays similar or ticks up slightly — you're buying MORE cooling in cheap hours to buy less in expensive ones. The win is on the bill, not the meter. On a flat-rate plan there is no win, which is why step one is knowing your plan.
Monsoon afternoons test it
When humidity spikes in late July and August, a coasting house gets muggy as well as warmer — the AC isn't running, so it isn't wringing moisture out of the air. Supercoolers with humidity sensitivity often shorten the coast window during monsoon weeks.
Comfort drift is real — plan for the people
The house will ride up several degrees through the peak window by design. For most households that's a fan and a cold drink; for heat-vulnerable people — elderly family members, medical conditions, some pets — riding to 82° may not be acceptable. In Phoenix heat, people beat rate math, every time.
Get Paid to Automate It
The smart thermostat that runs your supercooling schedule also earns bill credits — verified 2026-07-14.
Both utilities pay you to enroll the thermostat
Smart thermostat credits (SRP BYOT)
$50 + $25/seasonEnroll an eligible smart thermostat and SRP credits your bill $50 per device (up to two), plus $25 per device at the end of each May–October conservation season you stay enrolled.
Verified 2026-07-14 · SRP smart thermostat rebates
Smart thermostat credits (APS Cool Rewards)
$50 + $35/yrAPS discontinued its residential equipment rebates on Jan 1, 2026 — Cool Rewards is what remains: a $50 one-time enrollment credit plus $35 per season for each enrolled smart thermostat that participates in summer conservation events.
Verified 2026-07-14 · APS Cool Rewards
Thermostats we install: see the smart thermostat lineup
Straight Answers
Supercooling questions, answered
Answered with verified plan facts
Want supercooling set up right for your house?
We confirm your utility and plan, set the thermostat schedule, and — if the house can't hold its cold — show you exactly which envelope fix pays first.