Free homeowner tool
AC size calculator for Long Island homes
Answer six questions and get an estimated tonnage range, BTU target, and 2026 installed price band — then check any quote you've received against it.
Your home
Count only heated/cooled space. Skip an unfinished basement or garage.
Your estimate
Estimated system size
2.5–3 tons
Roughly 34,000 BTU (22.5 BTU per sq ft over 1,500 sq ft)
Standard efficiency installed
$7,200–$10,200
Variable-speed / high efficiency
$11,000–$14,500
2026 Long Island installed price bands on serviceable ductwork. Duct modifications and electrical upgrades add $1,800–$4,200.
This is a rule-of-thumb estimate, not a load calculation. It's built to tell you whether a quote you've been given is in a sensible range. Correct tonnage comes from a room-by-room Manual-J load calculation plus a static-pressure reading on your existing ductwork — both included free with every installation estimate we give.
How AC sizing actually works on Long Island
One ton of cooling equals 12,000 BTU per hour. A Long Island home typically needs 18–26 BTU per square foot, and where you land inside that range depends far more on the building than on its size. Original single-pane windows, thin attic insulation, a west-facing wall of glass, a dormer that added volume without adding returns — each moves the number meaningfully.
That's why two identical-looking Levitt capes on the same street can need different systems. It's also why the most common problem we're called to fix isn't an undersized AC — it's an oversized one, cooling the thermostat fast, shutting off before it dehumidifies, and leaving the house cold and clammy through August.
What a proper sizing visit includes
- 1.Room-by-room Manual-J heat gain: window area and orientation, insulation levels, ceiling volume, infiltration, and occupancy.
- 2.Static pressure and airflow test on existing ducts — each ton needs roughly 350–400 CFM to perform as rated.
- 3.Electrical check: panel capacity, breaker sizing, and disconnect condition, which decides whether an upgrade belongs in the quote.
- 4.Equipment selection: matched AHRI-certified condenser, coil, and air handler, with coated coils on South Shore homes exposed to salt air.
AC sizing questions Long Island homeowners ask
What size central AC do I need for a 1,500 sq ft house on Long Island?
Most 1,500 sq ft Long Island homes land between 2 and 2.5 tons (24,000–30,000 BTU). An unexpanded cape with updated windows can be right at 2 tons, while a sunny split-level with original windows can need 2.5. The only way to know is a Manual-J load calculation.
Is bigger always better for air conditioning?
No — oversizing is the most common sizing mistake we're called to correct. An oversized system satisfies the thermostat quickly, shuts off, and never runs long enough to pull humidity out of the air. The result is a house that's cold and clammy, plus more wear from short-cycling.
How accurate is this AC size calculator?
It's a rule-of-thumb estimate meant to tell you whether a quote you received is in a sensible range. It cannot replace a Manual-J calculation, which measures each room's windows, orientation, insulation, duct leakage, and infiltration.
What is a Manual-J load calculation?
Manual-J is the industry-standard room-by-room heat gain calculation published by ACCA. It's what determines correct tonnage, and New York mechanical codes reference it. We run one on every installation estimate at no charge.
Does my ductwork limit what size AC I can install?
Yes. Every ton of cooling needs roughly 350–400 CFM of airflow. If the existing trunk and returns can't move that, a larger condenser won't cool better — it will just short-cycle and freeze the coil. We measure static pressure before recommending tonnage.
Do humid Long Island summers change the sizing?
They change equipment choice more than tonnage. Our coastal humidity is why two-stage and variable-speed systems perform noticeably better here — long low-capacity runtimes remove far more moisture than a single-stage unit cycling on and off.
How much does installation cost once I know the size?
In 2026 on Long Island: about $5,800–$8,400 for a 2-ton standard-efficiency system, $8,500–$12,500 for a 3-ton, and $12,500–$18,500 for premium variable-speed equipment. Ductwork changes and electrical upgrades add $1,800–$4,200.