What does a heat pump cost to run per month in a Phoenix summer?

By Michael Fitzgerald, Founder & Editor, Phoenix Cooling Guide
Technically reviewed by Tom Mattingly, Owner & President, AZ Trusted Air LLC (ROC 317368)
Published 2026-09-18

Most heat pump running-cost articles were written for a climate where the machine heats for six months and cools for three. In the Phoenix metro the ratio inverts. The cooling season runs April into October, a July attic sits at 150 to 170 degrees above the ductwork, and the heating season amounts to a few weeks of cool nights. That changes which number matters. For a Valley homeowner, a heat pump's summer running cost is a cooling question, and its winter running cost is almost entirely a question of whether the auxiliary electric resistance heat is being allowed to run when it is not needed.

The other half of the answer is not equipment at all. It is the rate. The same kilowatt-hour costs a different amount depending on which utility serves the address, which price plan the household is on, and in SRP's case which of its billing seasons the month falls in. This page sets out the published rate structures, what is genuinely documented about savings, and what is not documented at all — because the figures circulating online for Phoenix heat pump operating cost are largely modelled, not measured.

Will my winter electric bill spike with heat pump heating?

Phoenix heating demand is small next to cooling demand. The Valley heating season is a handful of cool weeks when overnight lows drop into the forties and daytime highs recover into the sixties, against a cooling season that runs April into October. A heat pump in heating mode reverses its refrigerant cycle and moves heat from the outdoor air into the house, which takes far less electricity than creating the same heat with a resistance element. In most Phoenix homes a January bill on heat pump heating sits well below a July bill on cooling, and frequently below the shoulder months of May and October.

The spike homeowners actually experience comes from auxiliary heat: electric resistance strip heat in the air handler that energises when the thermostat calls for more heat than the compressor is delivering. A strip element turns one kilowatt-hour of electricity into one kilowatt-hour of heat, while the compressor delivers several times that from the same kilowatt-hour. A thermostat left in emergency heat mode, a deep overnight setback recovering at six in the morning, or an aggressive balance-point setting can all keep the strips energised in weather a Phoenix heat pump handles unassisted. Lockout temperatures are an installer setting, and most thermostats display an auxiliary-heat indicator worth checking.

Rate structure matters as much as equipment. APS's non-time-of-use residential option prices energy by annual usage tier rather than by hour: 12.925 cents per kilowatt-hour for 600 kWh or less, 14.052 cents for 601 to 999 kWh, and 15.418 cents at 1,000 kWh or more — a spread of 2.493 cents per kilowatt-hour from the lowest tier to the highest. Per APS's service plan FAQs, those prices apply regardless of time of day or day of week and are the same year-round, and the tier is based on average monthly use across the year. APS sets the tier from past annual usage, reviews usage annually, applies any reassignment starting with the January bill, and offers a one-time waiver to keep the current tier. That review is the mechanism by which a household that just added heat pump heating can find its price per kilowatt-hour has moved.

How does heat pump efficiency compare to my old AC on a time-of-use plan?

SRP describes SEER as a measure of how efficiently a central cooling system runs across an entire cooling season, calculated by dividing the cooling output of the air conditioner or heat pump by the energy it uses in kilowatt-hours — the higher the rating, the more comfort per dollar spent. The word doing the work there is seasonal. A seasonal average blends mild April afternoons with a 115-degree June afternoon, which is why the Southwest region's federal standards add EER2, a full-load measure, on top of SEER2. For a Phoenix homeowner comparing an old unit with a new one, EER2 describes the hour that actually strains the grid and the bill.

On a time-of-day plan, two homes with identical equipment and identical monthly kilowatt-hours can pay different amounts. SRP's Conserve 6-9 p.m. and Save plan lets customers save by limiting energy use during the more expensive on-peak times, weekdays 6 to 9 p.m. year-round, with lower prices during all other weekday hours, weekends and six observed holidays. APS's time-of-use option is built around a shorter weekday on-peak window earlier in the afternoon, so the two utilities do not share a peak period; the exact hours and prices for an address belong on that utility's own rate schedule and should be read there rather than inferred from the neighbouring utility.

SRP's own customer guidance is the clearest statement of how to exploit this. SRP says nearly half of the energy used in a home goes to heating and cooling, and advises installing a programmable or smart thermostat and pre-cooling: three hours before on-peak hours begin, set the thermostat three degrees below the preferred temperature. That instruction is easier to follow with a newer system. An older single-stage unit that is already marginal on a 115-degree afternoon has nothing in reserve to pull the house down three degrees ahead of the window, while a system with capacity to spare does it and then coasts through on-peak with the compressor mostly off.

For Phoenix-area homeowners who want this looked at on their own system, Phoenix Cooling Guide recommends AZ Trusted Air LLC (ROC 317368), whose owner Tom Mattingly reviews this guide. (623) 252-6403 · second opinion on a quote.

What annual savings can I realistically expect switching from an older AC and electric heat?

Start with the gap, because it is the most useful thing on this page. There is no published, measured figure for kilowatt-hours per month for a heat pump in a Phoenix summer, and no independent Arizona study of realised savings after a changeout. Numbers presented that way online are modelled outputs. The substitute is a homeowner's own billing history, which both SRP and APS publish in the online account: pull twelve months of kilowatt-hours, take a mild month such as March or November as the non-cooling baseline, and treat the excess above that baseline in each summer month as cooling energy. Multiply that excess by the applicable rate and the current cooling cost stops being a guess.

Then apply the rated arithmetic, with its limits stated. Because SEER is output divided by energy, moving from a 10 SEER unit to a 15 SEER unit cuts rated cooling energy for the same output by roughly one third — that is division on the definition, not a survey result. Two cautions apply. The SEER2 test procedure that replaced SEER in 2023 uses tougher conditions, so old SEER numbers and new SEER2 numbers are not directly comparable, and published summaries of the federal heat pump minimum disagree, with some citing 14.3 SEER2 and 7.5 HSPF2 and others a higher Southwest figure. The number that governs a specific job is the AHRI certified rating of the matched indoor and outdoor combination on the quote.

Savings leak in the attic before they reach the room. SRP cites the ENERGY STAR figure that in a typical home about 20 percent of the air moving through the duct system is lost to improper sealing — and in the Valley that air is lost into a space running 150 to 170 degrees in July, so the penalty is not just volume but temperature gain on what survives. SRP's Duct Test and Repair Rebate covers 75 percent of repair costs or up to $400 for duct testing and qualified repairs, which makes duct work one of the few running-cost measures with a published subsidy attached. Monsoon dust packing an outdoor coil is the other quiet cost, and it is free to wash off.

Incentives now change the answer in the other direction. The federal Section 25C Energy Efficient Home Improvement Credit, which carried a separate annual limit of $2,000 for heat pumps with no lifetime cap, is allowed only for property placed in service through December 31, 2025, per the IRS instructions for Form 5695. The Residential Clean Energy credit, the 30 percent credit that covered geothermal heat pumps and battery storage, ends on the same date. A 2026 Phoenix buyer should therefore price the job with no federal credit in it. What remains is utility side: through SRP's Cool Cash program, customers can take rebates up to $1,125 on a new energy-efficient air conditioner, heat pump or mini-split. APS equipment rebate availability has been reported as changing, so the status for an APS address should be confirmed with APS directly before it is written into a payback calculation.

How does two-stage or variable-speed change heat pump running costs?

The mechanism is straightforward. A single-stage compressor has one output: everything. It satisfies the thermostat, shuts off, and starts again, and every start carries an inrush and a period before the coil reaches steady-state efficiency. A two-stage unit has a lower gear; a variable-speed inverter unit has a continuous range. In a Phoenix July, when the outdoor temperature sits near design conditions for hours, all three run long anyway and the gap narrows. In April, May and October — months that are still cooling months here — the modulating system runs quietly at low capacity where the single-stage unit short-cycles, and the variable-speed blower draws a fraction of full-speed power at reduced airflow.

Sizing decides whether any of this is realised. An oversized variable-speed system spends its life in the upper part of its range because it was specified for a load the house does not have, and it then cycles much like the single-stage unit it replaced. Phoenix design conditions of roughly 115 degrees make oversizing tempting, and rule-of-thumb sizing by square footage almost always overshoots. Utility quality-install paperwork in Arizona has required contractors to size equipment to a calculated cooling load within a stated tolerance, which is a reasonable standard for a homeowner to borrow: ask for the Manual J calculation, on paper, for the specific house rather than a generic figure.