The Formula, Demystified
Cooling capacity in BTU per hour (tonnage × 12,000) divided by SEER2 gives the watts the system draws while running. A 3-ton system: 36,000 BTU ÷ SEER2 15 ≈ 2,400 watts — 2.4 kWh for every hour of runtime. Multiply by your FPL rate from the bill and by the hours it actually runs, and the month's cooling cost stops being a mystery. (Variable-speed systems complicate the per-hour figure — they sip at low output — but the season-long SEER2 math still holds.)
What Runtime Actually Looks Like Here
Broward cooling runs roughly ten months, with summer systems commonly running 8-12+ hours of compressor time a day — more in heat waves, in leaky homes, and with low setpoints. That runtime number is the lever nobody computes: the same 2.4-kW system at 8 versus 12 daily hours is a meaningfully different monthly bill. Smart thermostats that report runtime turn this from estimate into data; your utility's hourly usage graph does too.
Reading Your Own System's Numbers
The data plate on the condenser gives tonnage (often encoded in the model number — 36 means 36,000 BTU means 3 tons) and the system's rated efficiency; your AHRI match certificate has the precise SEER2. Older systems: a unit rated SEER 10 in 2008 is likely performing below that today — coils foul, charge drifts. The honest per-hour figure for an aging system is worse than its birth certificate, which is exactly what a maintenance visit's measurements reveal.
What "Too Much" Actually Means
Three comparisons answer it: against your own history (this June versus last June, weather-adjusted — your utility's data makes this easy); against the formula (if measured usage far exceeds tonnage-and-SEER2 math at your runtime, the system is drawing more or cooling less than rated — a health problem); and against replacement math (when an aging SEER 10-class system's monthly penalty versus a SEER2 15.2+ replacement starts paying real money toward the new system, the calculator conversation begins). Our operating-cost calculator runs all three; bring your bill.
The Cheap Wins Before The Big Decision
Before any replacement math: filter, coil cleaning, charge verification, and duct sealing all lower the watts-per-cooling ratio of the system you already own — the maintenance visit frequently buys back its cost in runtime. Setpoint discipline (each degree is real money at these runtimes) and fan-AUTO finish the free tier. Then, if the system is old and the math still hurts, the 14-vs-16 SEER2 guide and the FPL $200 rebate carry the replacement conversation — calmly, with your own numbers in hand.
Per-Hour Running Cost By System (At Your Rate)
Watts drawn = tonnage × 12,000 ÷ SEER2. Cost = kW × your per-kWh rate.
| System | Approx. draw running | Per-hour cost formula |
|---|---|---|
| 2-ton, SEER2 15 | ~1.6 kW | 1.6 × your rate |
| 3-ton, SEER2 15 | ~2.4 kW | 2.4 × your rate |
| 3-ton, SEER2 16+ | ~2.2 kW or less | 2.2 × your rate |
| 3-ton, aging SEER ~10 actual | ~3.6 kW | 3.6 × your rate — the upgrade argument |
| 4-ton, SEER2 15 | ~3.2 kW | 3.2 × your rate |
Compute Your Own Cooling Cost
- Tonnage from the condenser model number (÷12 of the BTU code).
- SEER2 from the AHRI certificate or data plate.
- Watts = tonnage × 12,000 ÷ SEER2; kWh/hour = watts ÷ 1,000.
- Runtime from your smart thermostat or utility hourly data.
- Multiply by your bill's per-kWh rate — then run the calculator.
Authoritative Sources
Need help from Abraham AC?
For AC repair, replacement, maintenance, indoor air quality, plumbing, or water heater service in Fort Lauderdale, Oakland Park, and Broward County, call Abraham AC.
Schedule ServiceFAQs
How many watts does a 3-ton AC use?
Roughly its 36,000 BTU divided by its SEER2 — about 2,400 watts running for a SEER2 15 system, less for higher tiers, more for aging units performing below their rating. The data plate and AHRI certificate hold your exact numbers.
How much does AC cost per day in Florida?
Draw (kW) × runtime hours × your rate. A 3-ton SEER2 15 system running 10 summer hours uses about 24 kWh a day — multiply by the per-kWh rate on your FPL bill for your number. Runtime is the swing variable.
Does an old AC really cost more to run?
Twice over: it was rated less efficient when new, and fouled coils, drifting charge, and tired components push it below even that. The measured gap between an aging system and a SEER2 15.2+ replacement is the honest core of every upgrade conversation.
Is a variable-speed AC cheaper to run?
Across a season, generally yes — modulating low for long stretches uses less energy than blast-and-stop, and its SEER2 rating reflects that. Its per-hour draw varies by output, so judge it on monthly usage, not a single hour.
What uses more electricity, the AC or the pool pump?
In summer, the AC — by a wide margin in most homes. But an old single-speed pool pump on a long schedule is routinely the second-biggest line and the cheapest big fix (variable-speed pumps). Your hourly usage data will show both signatures.
Can I lower the cost without replacing the AC?
Yes — in payback order: filter and coil care, charge verification, duct sealing, setpoint discipline, and fan-AUTO. Together they attack both the watts and the runtime sides of the formula. Replacement math comes after the cheap wins, not instead of them.
