Reference data
Heating and cooling load by climate zone
Screening BTU per square foot for each of the eight climate zones, and what it works out to in tons for common house sizes.
Written and edited by Pablo Ruiz Quintero
Last reviewed 2026-09-16
How many BTU per square foot do I need in my climate?
Between about 12 and 30 BTU/h per square foot for cooling, depending on where you are — and the honest answer is that it is a range within each zone too, because two houses of the same size in the same city can differ by a third on insulation and glass alone.
| Zone | Where | Cooling BTU/ft² | Heating BTU/ft² |
|---|---|---|---|
| Zone 1 — hot, humid | Miami, Key West, Honolulu | 25–30 | 10–20 |
| Zone 2 — hot | Houston, Phoenix, New Orleans, Orlando | 23–28 | 18–28 |
| Zone 3 — warm | Atlanta, Dallas, Los Angeles, Charleston | 21–26 | 25–35 |
| Zone 4 — mixed | Washington DC, Nashville, Kansas City, Portland | 19–24 | 30–40 |
| Zone 5 — cool | Chicago, Denver, Boston, Detroit | 17–22 | 35–45 |
| Zone 6 — cold | Minneapolis, Burlington, Helena | 15–20 | 40–50 |
| Zone 7 — very cold | Duluth, Fargo, northern Maine | 14–18 | 45–55 |
| Zone 8 — subarctic | Fairbanks, northern Alaska | 12–16 | 50–62 |
Cooling tons by house size
| Zone | 1,000 ft² | 1,500 ft² | 2,000 ft² | 2,500 ft² | 3,000 ft² |
|---|---|---|---|---|---|
| Zone 1 | 2.1–2.5 | 3.1–3.8 | 4.2–5.0 | 5.2–6.3 | 6.3–7.5 |
| Zone 2 | 1.9–2.3 | 2.9–3.5 | 3.8–4.7 | 4.8–5.8 | 5.8–7.0 |
| Zone 3 | 1.8–2.2 | 2.6–3.3 | 3.5–4.3 | 4.4–5.4 | 5.3–6.5 |
| Zone 4 | 1.6–2.0 | 2.4–3.0 | 3.2–4.0 | 4.0–5.0 | 4.8–6.0 |
| Zone 5 | 1.4–1.8 | 2.1–2.8 | 2.8–3.7 | 3.5–4.6 | 4.3–5.5 |
| Zone 6 | 1.3–1.7 | 1.9–2.5 | 2.5–3.3 | 3.1–4.2 | 3.8–5.0 |
| Zone 7 | 1.2–1.5 | 1.8–2.3 | 2.3–3.0 | 2.9–3.8 | 3.5–4.5 |
| Zone 8 | 1.0–1.3 | 1.5–2.0 | 2.0–2.7 | 2.5–3.3 | 3.0–4.0 |
What these figures are
Screening numbers. They are compiled from trade sizing practice by climate zone and they are published as ranges on purpose, because the underlying quantity genuinely is one.
They are not a Manual J. A real load calculation works room by room from the actual construction, orientation, window specification and air leakage of your house, and it routinely lands twenty to thirty per cent away from any per-square-foot figure. Use these to judge a quote or set a budget; get a Manual J before anyone installs equipment.
Where the two loads cross
Read down the table and something useful appears: in zone 1 the cooling load is more than double the heating one, and by zone 6 it is the other way round. They pass each other around zone 4.
That crossover is the technical argument for a heat pump. A single machine that heats and cools makes most sense where the two loads are similar, because it is sized once and used hard in both directions. It is also why the southern half of the country adopted them long before the north did.
The trap in the tonnage table
The second table is the one that gets misused. It is an average house — 8 ft ceilings, ordinary insulation, ordinary glass. A 1970s house with original walls needs roughly a quarter more; a well-sealed modern one needs a third less. That spread is wider than the difference between two adjacent climate zones, which is exactly why square footage alone is not a sizing method.
Using it
The BTU calculator applies these figures with adjustments for insulation, glazing, sun, ceiling height and occupancy, and then picks the smallest manufactured equipment size that covers the load — rather than the next one up, which is the habit that makes houses cold and clammy.
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About the author
Pablo Ruiz Quintero — Editor
Editor of MaterialsEstimator. Decides which documents count as a source, what every default value is, and where the line sits between what the reader parses and what the engines compute.
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