The short answer: about $136 a month for a 3-ton system at current PECO rates
A 3-ton central air conditioner at Pennsylvania’s current minimum efficiency, running about eight hours a day through a humid Delaware County July, costs roughly $136 a month to run at PECO’s current combined rate of about 22.1 cents per kilowatt-hour. An older 10 SEER unit doing the same work in the same house costs closer to $191 a month a difference of roughly $55 in every peak cooling month.
Those are real numbers built from PECO’s published rates rather than a national average, but they are an illustration, not a promise. What you actually pay depends on four things working together: the size of your unit, how efficient it is, how many hours a day it actually runs, and what PECO charges per kilowatt-hour on your specific rate schedule. There is no single average number that applies to every house on your street, even if the house next door looks identical. A 2,000-square-foot colonial in Havertown with an original SEER 10 condenser from the 1990s and a 2,000-square-foot colonial with a new 15 SEER2 system are not running the same bill, even on the same hot July day. The rest of this page shows you how to adjust the figures above to your own house instead of borrowing a national average that was never built with Philadelphia-area summers in mind.
The Real Formula Behind Your AC Bill
Every dollar you spend running central air comes from the same equation: tonnage x efficiency rating x daily runtime hours x your PECO rate per kWh. Change any one of those four inputs and the monthly cost moves with it.
- Tonnage is how much cooling capacity your system has. Bigger homes generally need more tons, but a poorly sized unit (too big or too small for the house) runs inefficiently either way.
- SEER or SEER2 rating SEER2 (or the older SEER) rating tells you how much cooling you get per unit of electricity. A higher number means less electricity for the same amount of cooling. SEER2 is the current standard: it is tested under higher static pressure than the old SEER scale and reads roughly 4 to 5 percent lower for the same equipment, so the two are not interchangeable.
- Daily runtime hours depend on outdoor temperature, humidity, your thermostat setting, insulation, duct condition, and how many hours the house is occupied and cooled.
- PECO’s rate per kWh is the dollar figure that turns all of the above into an actual bill. It changes periodically and shows up as more than one line item on your statement.
Generic online calculators plug in a national average electricity price and a flat assumption for cooling hours. Neither of those reflects Delaware County. Your actual cost is the product of your real tonnage, your real SEER rating, your real runtime, and your real PECO rate, not a national blend of all of those things.
What PECO Actually Charges (And How to Read It Off Your Bill)
PECO residential bills are not a single flat rate. They’re built from two separate charges that get added together: a supply charge (the cost of the electricity itself) and a delivery charge (the cost of delivering it to your house over PECO’s wires). Both charges are billed per kWh, and both show up as separate line items on your monthly statement. When you’re trying to figure out what your AC is costing you, you need to add those two per-kWh charges together, not just look at one of them, because the “rate” that matters for your runtime calculation is the combined total.
Your bill also shows your total kWh usage for the billing period. If you want a rough read on what cooling is costing you specifically, compare your kWh usage in a peak summer month against a mild spring or fall month with the AC off. The difference in usage, multiplied by your combined PECO rate, is a reasonable estimate of what your central air is adding to the bill that month.
Home Size, System Age, and the SEER Gap
Instead of publishing a single dollar table that can’t possibly be accurate for every house in Delaware County (your rate, your tonnage, and your runtime are unique to your home), here’s the comparison that actually matters: how much less electricity a current SEER2-minimum 15 system uses than an older SEER 13 unit doing the same job. Pennsylvania sits in the federal North efficiency region, where the minimum for a new split-system central air conditioner is 13.4 SEER2 roughly 14 on the old SEER scale. That is the legal floor, not the target. The 15 SEER minimum you will see quoted on national sites applies to the Southeast and Southwest regions, not here.
SEER is a ratio of cooling output to energy input. A system rated SEER 15 produces the same cooling as a SEER 13 system while using roughly 13 percent less electricity to do it, because 13 divided by 15 is about 0.87. If your home still runs on an original SEER 10 to 13 unit from the pre-2006 or pre-2015 efficiency eras, the gap against a current SEER2 15 system is even wider. That percentage applies across home sizes, from a 1,500-square-foot cape to a 3,000-square-foot colonial. A bigger home needs more tons and therefore uses more total kWh to cool, but the percentage savings from upgrading an old, inefficient unit to a current one holds steady regardless of square footage.
Most Delaware County homes replacing a condenser are coming off a unit in the 10 to 12 SEER range, which is where the gap is widest. If that is you, the meaningful comparison is not against the legal minimum it is against a premium 16 to 18 SEER2 system, where you are looking at saving something closer to a third of your cooling electricity rather than a few percent. The percentage holds across home sizes: a bigger home needs more tons and uses more total kWh, but the proportional saving from replacing an old unit stays roughly the same whether it is a 1,500-square-foot cape in Drexel Hill or a 3,000-square-foot colonial in Springfield.
The practical takeaway: if your central air is more than 15 years old, you are very likely paying a meaningful premium every single cooling month just to run equipment that’s less efficient than what’s standard today, on top of whatever repair costs an aging system is already racking up.
Why Delco’s Climate Changes the Math
National AC cost calculators assume a generic number of cooling hours per day, and that number usually comes from a national blend of dry, mild, and humid climates averaged together. Delaware County isn’t any of those on its own. Philadelphia-area summers run humid, and humidity makes an air conditioner work harder for the same thermostat setting, because the system has to pull moisture out of the air in addition to lowering the temperature. That means your actual runtime hours on a 90-degree, humid July day in Delco are higher than what a generic calculator assumes for a “typical” hot day anywhere in the country.
This is also why two houses with identical SEER ratings and identical tonnage can post different bills in the same month. Shade, insulation, duct leakage, and how tightly the house is sealed all change how many hours the compressor has to run to hit the thermostat setpoint, and in our climate those hours add up fast during peak summer stretches.
5 Ways to Cut the Bill Without Buying a New System
- Raise the thermostat a few degrees and use a schedule. Every degree closer to the outdoor temperature reduces runtime hours, which is the single biggest lever in the formula.
- Change the filter on schedule. A clogged filter restricts airflow, forcing the system to run longer to move the same amount of cool air through the house.
- Seal leaky ductwork. Ducts running through an unconditioned attic or crawlspace in an older Delco home can leak cooled air before it ever reaches a vent, which means more runtime to compensate.
- Get an annual tune-up. A system with low refrigerant charge or a dirty coil has to run longer to hit the same temperature, which quietly inflates the bill all season.
- Consider zoning. If you’re only cooling the rooms you actually use during the day, you’re not paying to run cold air through empty bedrooms. Our mini-split vs. central air comparison for Delco’s older homes covers zoning options worth considering for houses with uneven cooling needs.
When a High Bill Means It’s Time to Replace, Not Repair
If your cooling-season bills keep climbing year over year even though your habits have not changed, and the system is already old enough that you are calling for repairs most summers, the math is working against you from two directions: rising repair costs and a widening efficiency gap against current equipment. At that point, the electricity you’re overpaying for every month is effectively financing the old system’s inefficiency instead of going toward a replacement that would lower that bill permanently. Check our Cooling page for what a properly sized, current-efficiency system looks like for a Delco home, and look at the HVAC rebates and tax credits available in Delaware County for 2026 before you price anything out, since those can offset a meaningful chunk of the upfront cost.
FAQ
Does a bigger AC cost more to run?
A properly sized bigger unit cooling a bigger house will use more total kWh than a smaller unit cooling a smaller house, simply because it’s moving more cooling capacity. But an oversized unit for the actual square footage can cost more to run than a correctly sized one, because it short-cycles instead of running efficient, longer cycles. Size matters less for cost than whether the tonnage actually matches the house.
Does lowering the thermostat raise the bill faster than it seems like it should?
Yes. The relationship isn’t linear in a Delco summer, because a lower setpoint means more runtime hours, and in high humidity the system also has to work harder per hour to pull moisture out of the air. A few degrees lower can translate into a disproportionate jump in runtime, and therefore cost, during the most humid stretches of July and August.
Is a heat pump cheaper to run than central air in Delco?
For cooling specifically, a heat pump and a central air system with the same SEER2 rating run at the same cost, because a heat pump in cooling mode works the same way a standard AC condenser does. The cost difference between the two shows up on the heating side, not the cooling side. If you’re weighing the two options for a Delco home, our mini-split vs. central air guide walks through that comparison in more detail.
Get a Free Efficiency Check in Delaware County
If you want an actual number for your own house rather than a worked example, we can go through your system’s tonnage, its age and your current PECO usage, and tell you where your bill is coming from and whether a repair, a tune-up or a replacement makes the most financial sense. Reach out through our Contact Us page, and if a new system turns out to be the right move, check our financing options to see how the monthly payment compares against what you are already losing to an inefficient unit every summer.