Arizona keeps two heating ledgers. The Valley's is nearly blank: a token winter, design nights in the upper thirties, where every dollar of fixed heating cost weighs heavily per useful hour because there are so few useful hours to spread it across. The high country's is real: Flagstaff, Show Low, Prescott, and the mountain towns run genuine winters where heating is a working line item, and where propane trucks serve households the gas mains never reached. This guide runs the conversion arithmetic for both ledgers and every legacy fuel on them: the strip heat wired into older Valley stock, the gas furnaces on the Southwest Gas mains, the propane tanks at elevation, and the oil holdouts, which in this state are rare enough to be folded into the delivered-fuel case. In the Valley, the cooling calendar settles every comparison; in the mountains, the fuel math does.
The Ledger in One Table
| Existing heat | Case for a heat pump | Strength |
|---|---|---|
| Electric strip heat | Same meter, a half to a third the consumption | Strongest |
| Propane (high country) | Usually the state's most expensive delivered heat | Strongest |
| Aging heat pump or AC | Modern variable-speed machine out-cools it all season | Strong |
| Heating oil | Truck-priced fuel loses to metered kilowatt hours | Strong, rare |
| Natural gas | Closest race; the cooling calendar settles it | Honest maybe |
Strip Heat: The Multiplication That Never Misses
Electric resistance converts one unit of electricity into one unit of warmth, at full price, every hour it runs. A heat pump on the same meter at the same rate moves two to three units of warmth per unit purchased, so the heating share of the bill simply shrinks toward a half or a third, with no fuel forecast anywhere in the calculation. In the Valley's older stock, the midcentury blocks of central Mesa, Glendale AZ, and Tempe, and the conversions and casitas scattered through the core, strip kits and wall heaters still carry the token winter, and the conversion case is the strongest in the metro. The absolute dollars are modest because the winter is, but the same machine then spends the other ten months being a better air conditioner than whatever it replaced, which is where the real money was all along.
Propane at Elevation: The Truck Stops Coming
The high country holds the state's serious heating bills. Past the gas mains, around Payson AZ, Show Low, Pinetop, and the rural stretches of Yavapai County and Coconino County, households buy heat in tank fills at prices that swing with a market they cannot negotiate with. A cold-climate heat pump replaces those gallons with kilowatt hours that move two to three units of heat apiece, billed monthly at rates that move slowly, and the saving lands in four figures for most conversions. The specification differs up there: real winters demand machines chosen for genuine cold-night capacity, per our cold-weather guide, and the arithmetic still clears, because propane's per-unit cost gives the heat pump the widest margin of any fuel on this page. The rare oil holdout reads the same truck-versus-meter math with the same verdict.
The Aging Machine Problem
The Valley's boom rings, Chandler, Gilbert, Peoria, Surprise, Queen Creek, San Tan Valley, carry an enormous population of builder-grade air conditioners and heat pumps installed by the subdivision, aging on the schedule they were built on, plus the midcentury stock's older equipment running on borrowed time. The old machine's bill signature is a summer problem here: cooling bills a modern variable-speed unit would beat month after month through the longest season in the country. The winter side barely registers, which is exactly the point: in a cooling-dominated calendar, replacing a tired machine with a right-sized variable-speed heat pump upgrades the biggest line on the energy year, and the heating improvement rides along free, per our installation cost guide.
The Honest Gas Paragraph
A household with a functioning furnace on the Southwest Gas mains faces the closest race in this guide, and deserves it stated coldly. Gas is cheap heat, and displacing a mid-life furnace rarely pays on fuel savings alone, least of all in a Valley climate that asks the furnace for a few weeks of work a year. The conversions that clear anyway are calendar cases, and no calendar argues louder than this one: the cooling equipment works from spring past October, dies on schedule, and its replacement dollar buys a machine that heats too, which is how most Valley gas households end up with a heat pump without ever deciding to electrify. Dual fuel is a legitimate configuration a good contractor prices without being asked, and it earns real keep in the high country. What no honest bidder does is promise a Valley gas household dramatic heating savings; a bid that does has failed the first test in our contractor guide.
The Cooling Side Carries the Payback
Every Valley case above rides on the same fact: here the heat pump spends nearly its whole life being a better air conditioner, through a season that runs longer and harder than anywhere else it could be asked to. The air conditioner was already the dominant line on the electric bill, a right-sized variable-speed machine beats old equipment through every hour of it, and that is where the payback actually lives. The heating savings are the bonus; the cooling improvement is the job, and it is the reason even the closest race in the table resolves in the heat pump's favor at replacement time.
Reading the First Year Correctly
Judge a conversion by shape, not by a single statement. The propane convert at elevation sees a larger winter electric bill and a smaller year, because the truck line vanished. The strip-heat convert sees the same warmth cheaper immediately. The replacer of an old machine sees the summer improve, which in the Valley is nearly the whole year. The discipline that makes all three legible is one ledger: last year's total heating and cooling spend, every source, next to this year's, read whole year against whole year. A single winter statement is the wrong number in a state that spends its real money from May past September.
The Rebate Layer, Held Lightly
The utility money is mapped in our rebates guide: SRP's Cool Cash pays up to $225 per ton for variable-speed machines, topping out at $1,125 at five tons; TEP takes up to $720 off instantly in Tucson through participating contractors; and APS pays nothing, its program having ended January 1, 2026. The federal 25C and 25D credits ended December 31, 2025. None of it changes any verdict in this guide; the arithmetic stands on fuel and calendar alone, and the rebate is a pleasant final line on a project that already cleared.
Renters, Landlords, and the Split Incentive
The Valley's worst cooling disproportionately serves people who cannot replace the equipment: tired package units and window units on older rental stock, strip heat in conversions, all billed to tenants through the hardest cooling season in the country. The tenant pays the bill; the owner owns the fix; and the arithmetic reads identically for both, with only the beneficiary line changing. The owner's case needs no charity: a large operating improvement through a ten-month season, and a property that rents better for both. A tenant's cheapest move is forwarding this page to whoever holds the deed.
One Rule Before Any Conversion
Every case above assumes the machine was specified for its actual climate: in the Valley, sized to hold on the hottest design day of the year with the token winter checked in passing; in the high country, chosen for genuine cold-night capacity against a real heating load. Published capacity tables beside a room-by-room load calculation, backup sized as a safety net rather than a crutch, and placement that respects the desert sun. The arithmetic in this guide is fuel arithmetic; the specification discipline is what keeps it true through the first 115-degree week and the first mountain cold snap alike.
The Short Version
Strip heat loses on a single bill's multiplication. Propane loses on truck-versus-meter arithmetic, hardest at elevation where the bills are real, and the rare oil holdout loses the same way. Aging machines lose on their summers, which in the Valley is nearly everything. Functioning gas furnaces make it a fair fight that the cooling calendar settles almost every time. The math carries every case from Arcadia to Ahwatukee to Flagstaff, and the machine that wins it spends its life doing the job Arizona actually hired it for.
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