Why Most Older Delaware County Homes Have an Oversized AC

A bigger AC is not a better AC. It’s louder, less comfortable, and shorter-lived than a properly sized one. And yet in older Delaware County homes, oversized systems are the rule, not the exception.

Here’s what’s going on, and what it means for your house.

What “oversizing” actually means

Air conditioners and heat pumps are rated in tons (one ton = 12,000 BTU/hr of cooling capacity). A system is oversized when its rated capacity is more than the home’s actual heat load on a design-day afternoon.

When a system is oversized:

It cools the room temperature to setpoint quickly, then shuts off
It doesn’t run long enough to remove humidity
The result is “cold and clammy” — temperature is right but the air feels wrong
It short-cycles: dozens of starts and stops per hour, which wears the compressor
It’s noisier on every cycle
It costs more upfront, and more to operate

In short: oversized is worse on every metric except marketing.

Why this is so common in older Delco homes

A few reasons stack up:

Rule-of-thumb sizing. Most contractors size off square footage with a multiplier (e.g., 600 sq ft per ton). That multiplier was developed for 1970s construction and grossly overestimates the load on newer or upgraded homes — which means basically every older Delco home that’s had any insulation, window, or air-sealing work done.

Worst-case thinking. “Better too much than too little” sounds responsible but isn’t. Too much is its own problem.

Replacement-in-kind. When an old system is replaced with the same size, the new one inherits all of the old oversizing — plus any improvements to the home over the decades.

Contractor incentives. Bigger systems cost more, and “we’ll get you the biggest unit we can install” sounds like a feature.

What right-sizing actually requires

A Manual J load calculation. This is a room-by-room calculation that accounts for:

Square footage and ceiling height
Insulation levels in walls, attic, and basement
Window area, orientation, and glazing
Infiltration / air-tightness
Internal heat gains (occupants, appliances)
Local design temperatures

A proper Manual J takes a few hours. It’s not optional — it’s the only way to size a system correctly.

What changes in older Delco homes

Once you do the actual calculation on a typical 1950s Havertown twin or a 1960s Broomall split-level, the result is almost always smaller than the existing system. Common findings:

A 3-ton AC replaced by a 2.5-ton variable-speed system that delivers better comfort
A 100,000 BTU furnace replaced by an 80,000 BTU two-stage condensing unit
A 4-ton heat pump where a 3-ton was originally proposed

The variable-speed factor matters too. A correctly-sized variable-speed system can run at 30–70% capacity for most of the day — the only way to actually control humidity in a Mid-Atlantic summer.

What to ask any contractor quoting a system

“Will you run a Manual J load calculation as part of the quote?” If the answer is no or “we have software that estimates it,” keep shopping.
“What’s the calculated load in BTU/hr, and how does that compare to the system you’re proposing?”
“What’s the airflow at the design condition, and does my existing ductwork support it?” A correctly-sized AC paired with under-sized ducts will still underperform.
“What’s the latent-to-sensible ratio of the proposed system?” Mid-Atlantic summers have meaningful humidity. The right system controls both.

We do Manual J on every install. It’s not a sales tactic — it’s how you get a system that lasts and works.