Room Air Conditioner BTU Size Guide

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Result

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What this result means

This tool performs a direct lookup from the ENERGY STAR room-air-conditioner sizing chart. It then applies only the four adjustments that the same public guidance specifies: heavy shade, strong sun, regular occupants beyond two, and kitchen use.

The result is a consumer shopping guide for a window or through-wall room AC. It is not a calculated heating or cooling load, it does not certify code compliance, and it is not suitable for selecting a portable air conditioner, ductless head, heat pump, or central system.

Published base capacity bands

These values assume an 8-foot ceiling. Square footage determines the starting capacity before the published adjustments are applied.

Room area	Base capacity
100–150 sq ft	5,000 BTU/hr
151–250 sq ft	6,000 BTU/hr
251–300 sq ft	7,000 BTU/hr
301–350 sq ft	8,000 BTU/hr
351–400 sq ft	9,000 BTU/hr
401–450 sq ft	10,000 BTU/hr
451–550 sq ft	12,000 BTU/hr
551–700 sq ft	14,000 BTU/hr
701–1,000 sq ft	18,000 BTU/hr
1,001–1,200 sq ft	21,000 BTU/hr
1,201–1,400 sq ft	23,000 BTU/hr
1,401–1,500 sq ft	24,000 BTU/hr
1,501–2,000 sq ft	30,000 BTU/hr
2,001–2,500 sq ft	34,000 BTU/hr

Why the guide stops here

A defensible whole-building load calculation must consider more than room area. Climate design conditions, walls, windows, air leakage, humidity, ducts, internal loads, and the selected equipment's performance all matter. The US Department of Energy cautions that rules of thumb often oversize comfort systems; ACCA likewise states that only its approved software produces results compliant with its Manual J standard.

For ductless, heat-pump, central, whole-home, or code-submission work, use a qualified designer and verify the software on ACCA's approved-software list. This site does not claim to perform or approximate that procedure.

Source and update policy

The capacity bands and adjustments come directly from the public EPA ENERGY STAR room-air-conditioner guidance, last checked September 20, 2026. BenchCalcs stores the figures in a tested data file so a source change can be reviewed before the calculator changes.

Evidence & limits

Sources you can inspect

Looks up EPA ENERGY STAR's published room-air-conditioner capacity band for an 8-foot-ceiling room, then applies only its published adjustments for heavy shade, strong sun, regular occupants beyond two, and kitchen use.

ENERGY STAR room air conditioners — the capacity bands, 8-foot-ceiling assumption, and published sun, shade, occupancy, and kitchen adjustments
ACCA-approved software — the boundary between this consumer guide and a compliant professional load calculation

Model limit: This consumer guide is not an HVAC load calculation and cannot size heating, portable air conditioners, ductless mini-splits, heat pumps, central systems, or rooms outside the published chart's assumptions.

See how BenchCalcs reviews calculations and corrections and how it handles source freshness and licensing.

Related guide

What Is Manual J — and When You Need One When ENERGY STAR's room-AC guide is enough and when you need a professional residential load calculation.

Recommended gear

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ENERGY STAR-certified room air conditioners

Compare window and through-wall models near the guide's BTU result, then verify the manufacturer's room-size and installation instructions.

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FAQ

Questions, answered

What equipment does this guide size?

It is for a window or through-wall room air conditioner serving one enclosed room. It does not size heating, portable air conditioners, ductless mini-splits, heat pumps, or central systems.

Why does the guide not ask for climate or insulation?

ENERGY STAR's public consumer chart uses room area, then publishes adjustments for shade, strong sun, extra occupants, and kitchens. Climate, construction, air leakage, humidity, and equipment performance belong in a full HVAC load calculation, so this guide does not invent multipliers for them.

Does this replace a Manual J load calculation?

No. This is a consumer room-AC capacity lookup, not an ACCA Manual J calculation. Use a qualified HVAC designer and ACCA-approved software for ductless, heat-pump, central, or whole-home equipment.

What if my ceiling is higher than 8 feet?

The ENERGY STAR capacity chart assumes an 8-foot ceiling. A taller or vaulted room falls outside the chart's stated basis; follow the equipment manufacturer's guidance or obtain a professional load calculation.

Why not buy a larger unit just in case?

ENERGY STAR warns that an oversized room AC may cool the room before it removes enough humidity, leaving the space cool but damp while reducing efficiency.

How is sun exposure handled?

The published guidance reduces the base capacity by 10% for a heavily shaded room and increases it by 10% for a very sunny room. Choose average when neither description clearly fits.

How are people and kitchens handled?

The chart already allows for up to two regular occupants. Add 600 BTU/hr for each regular occupant beyond two, and add 4,000 BTU/hr when the unit will cool a kitchen.