Pick your county to fill the 99% heating design temperature from EPA’s ENERGY STAR reference guide, or type your own. Picking your county also sets its 2021 IECC climate zone (see the climate zone map).
The county sets the heating numbers (its official winter design temperature). Cooling uses the summer climate you pick, the same model as our area chart.
| Cooling load | — |
| Your quote | — |
| Heat loss | — |
| Gas furnace | — |
| Heat pump | — |
| Airflow | — |
| Main supply duct | — |
| Cooling cost / year | — |
Sizes shown are the ones inside ENERGY STAR’s recommended range: 90–115% of the cooling load for a single-speed unit, 90–130% for variable-speed. A size that only appears in the allowed range (up to 130% or 160%) is shown on its own.
| US summer climate | Cooling load | Single-speed AC | Variable-speed |
|---|---|---|---|
| Zone 1 — Hot (FL, S. TX, AZ desert) | 58,300 BTU/h | 5 ton | 5 ton |
| Zone 2 — Warm (Deep South, TX) | 52,000 BTU/h | 4 ton | 4–5 ton |
| Zone 3 — Moderate (TN, NC, MO) | 45,800 BTU/h | 3.5–4 ton | 3.5–4 ton |
| Zone 4 — Mild (Mid-Atlantic, Pacific NW) | 41,600 BTU/h | 3.5 ton | 3.5–4 ton |
| Zone 5 — Cool (Upper Midwest, New England) | 37,500 BTU/h | 3–3.5 ton | 3–4 ton |
Cooling load: the same whole-home model as our area chart (8 ft ceilings, average insulation and sun). It is a planning estimate; an ACCA Manual J calculation is the real number.
How common is 2,500 sq ft? Of the new single-family homes completed in the US in 2025, 18% had 2,400–2,999 sq ft of floor area and 62% were smaller. A 2,500 sq ft home is 17% larger than the median new home (2,142 sq ft), and 98% of those new homes were built with air-conditioning (U.S. Census Bureau).
Where a 4-ton heat pump heats it alone. In our heating model, a 4-ton cold-climate heat pump covers the whole heat loss of a typical 2,500 sq ft home down to an outdoor temperature of about 13°F (its balance point). 1,391 of the 3,144 counties in ENERGY STAR’s design-temperature list (44%) have a winter design temperature at or above that, so the heat pump needs no backup heat there. That includes every county in 11 states and territories, among them Alabama, Arkansas, District of Columbia, Florida, Georgia; in 22 — Colorado, Connecticut, Indiana, Iowa, Kansas, Maine and others — no county qualifies.
Heating depends on how cold your winters get far more than on floor area. Below: heat loss at five counties’ official winter design temperatures for a typical 1990s–2000s, one-story 2,500 sq ft home (our labelled assumption, not an official figure). Use the tool above with your county and house for your own number.
| Location | Winter design temp | Heat loss (Btu/h) | Furnace output range | Furnace input at 95% AFUE | 4-ton cold-climate heat pump covers |
|---|---|---|---|---|---|
| Miami (Miami-Dade County, Florida) | 48°F | 13,900 | 13,900–19,400 | 30,000* | 100% |
| Houston (Harris County, Texas) | 29°F | 25,800 | 25,800–36,200 | 30,000 | 100% |
| Atlanta (Fulton County, Georgia) | 20°F | 31,500 | 31,500–44,100 | 40,000 | 100% |
| Columbus (Franklin County, Ohio) | 5°F | 41,000 | 41,000–57,400 | 45,000 | 82% |
| Minneapolis (Hennepin County, Minnesota) | -11°F | 51,100 | 51,100–71,500 | 60,000 | 55% |
Design temperatures: ENERGY STAR county guide (99%). Furnace output: 100–140% of heat loss. Heat pump: cold-climate unit at 70% of rated capacity at 5°F; below 100%, backup heat covers the rest. *Smallest common furnace is over 140% of the loss: choose a modulating model or let the heat pump carry it. Full method.
In a moderate US climate a 2,500 sq ft home lands on 3.5–4 ton; in the hottest climates 5 ton; in cool northern ones 3–3.5 ton (single-speed, ENERGY STAR recommended range). Two-story homes this size often use two smaller systems or zoning so the upstairs does not run hot.
A 4-ton system moves about 1,600 CFM at the common target of 400 CFM per ton (Carrier), or 1,400–1,800 CFM across the 350–450 range ACCA describes for humid to dry climates. Carried in one round sheet-metal trunk at a 0.08 friction rate, that is a 18-inch main supply duct; most homes split it into a rectangular trunk and branches. See the duct CFM chart for branch sizes. Breaker and wire size come from the outdoor unit’s nameplate (MCA and MOCP), not the tonnage: see the ampere calculator.
Yearly electricity for a 4-ton system at $0.17/kWh, for three assumed amounts of use (full-load hours).
| Rating | Light use 500 h/yr | Moderate use 1,000 h/yr | Heavy use 1,500 h/yr |
|---|---|---|---|
| 13.4 SEER2 — Federal minimum (North) | $304 | $609 | $913 |
| 15.2 SEER2 — ENERGY STAR heat pump minimum | $268 | $537 | $805 |
| 18 SEER2 — High efficiency | $227 | $453 | $680 |
kWh = Btu/h × hours ÷ SEER2 ÷ 1,000. Your own rate and hours: AC bill calculator.
This page also covers 2,400 sq ft.
| Area | Cooling load (moderate) | Recommended AC | BTU per sq ft |
|---|---|---|---|
| 2,400 sq ft | 44,200 BTU/h | 3.5–4 ton | 18.4 |
| 2,500 sq ft | 45,800 BTU/h | 3.5–4 ton | 18.3 |
← 2,000 sq ft · 3,000 sq ft →
Other sizes (sq ft): 200 · 300 · 400 · 500 · 600 · 800 · 1,000 · 1,200 · 1,500 · 1,600 · 1,800 · 2,000 · 3,000 · full chart from 100 to 5,000 sq ft
India: homes are cooled room by room with split ACs, so this whole-home figure does not apply. Switch the tonnage calculator to India mode and size each room.
Same cooling model as the area chart, same heating model as the furnace calculator; neither replaces a contractor’s ACCA Manual J. Details on the methodology page.
About 45,800 BTU/h of cooling load in a moderate US climate, so 3.5–4 ton sits inside ENERGY STAR’s recommended range for a single-speed system. In the hottest US climates it is 5 ton; in cool northern ones 3–3.5 ton.
About 18.3 BTU per sq ft in a moderate climate (23.3 in the hottest, 15.0 in cool climates). Larger homes need fewer BTU per square foot because walls and roof grow more slowly than floor area.
In a moderate climate, yes: it is 131% of the cooling load, above ENERGY STAR’s 130% limit for a single-speed unit. In the hottest climates it is 103% of the load, which is within the limits.
It depends on your winter. A typical 1990s–2000s 2,500 sq ft home near Columbus, Ohio (design temperature 5°F) loses about 41,000 Btu/h, so a furnace with 41,000–57,400 Btu/h of output fits; near Minneapolis (-11°F) it is about 51,100 Btu/h. Pick your county in the tool for your own figure.
About $537 a year for a 4-ton, 15.2 SEER2 system running 1,000 full-load hours at $0.17/kWh (3,158 kWh). Hot climates run more hours; mild ones fewer.
About 1,600 CFM for a 4-ton system at 400 CFM per ton, or 1,400–1,800 CFM across the 350–450 range.
About 1,300–1,700 sq ft of a typical home in a moderate climate, and 1,000–1,300 sq ft in the hottest. For 2,500 sq ft it is only 66% of the moderate-climate load.
Usually not: 3 tons is 79% of the cooling load in a moderate climate, below ENERGY STAR’s 90% minimum, so it would fall behind on the hottest days. In cool northern climates it is 96%, inside ENERGY STAR’s recommended range (90–115%). Two-story homes this size often split the load between two smaller systems instead.
About 44,200 BTU/h in a moderate climate, so 3.5–4 ton (ENERGY STAR’s recommended range for single-speed). See the 2,400 sq ft row.
Official and manufacturer sources, checked October 2026.
actonnagecalc.com is not affiliated with, or endorsed by, the U.S. EPA, ENERGY STAR®, DOE or the ICC. Their publications are cited as sources.