Room and Window AC BTU Calculator
Select a room or window air conditioner from the ENERGY STAR floor-area capacity table, then apply transparent user-entered allowances. The published table covers 100 through 2,500 square feet and uses an eight-foot ceiling basis.
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View all saved project estimatesWhat does the AC BTU calculator calculate?
Multiply room length by width, then use ENERGY STAR’s room-area table for baseline cooling capacity. Apply your ceiling-height factor and shade or sun adjustment, add 600 BTU/h for each regular occupant beyond two, and enter any kitchen allowance. This screens room or window units; it is not a whole-house Manual J calculation.
ENERGY STAR room AC table with entered adjustments
Room floor area selects the published ENERGY STAR table capacity, whose stated basis is an eight-foot ceiling. The user-entered ceiling factor and published minus-ten-percent shade or plus-ten-percent sun adjustment modify that baseline. ENERGY STAR’s 600 BTU/h per additional regular occupant is then added with the entered kitchen allowance before practical rounding.
How to measure for an accurate estimate
- Measure and multiply the finished length and width of the single enclosed room; divide complex shapes into rectangles and triangles, then total their areas.
- Use a ceiling factor of 1.0 for the table’s eight-foot basis, and obtain a justified factor rather than assuming a linear adjustment for unusual ceilings.
- Choose minus 10% only for a heavily shaded room, plus 10% only for a very sunny room, or zero when neither ENERGY STAR condition applies.
- Count regular occupants beyond the first two and enter 4,000 BTU/h for a kitchen under the published guidance; otherwise enter zero.
Sunny kitchen with regular additional occupants
A 20-by-20-foot kitchen has 400 square feet, an eight-foot ceiling factor of 1.0, a plus-10% very-sunny adjustment, two regular occupants beyond the first two, and the ENERGY STAR 4,000-BTU/h kitchen allowance.
The table baseline is 9,000 BTU/h. Sun adds 10%, the two additional occupants add 1,200 BTU/h, and the kitchen adds 4,000 BTU/h, producing a rounded planning capacity of 15,100 BTU/h.Before you purchase material
- Avoid deliberate oversizing because an oversized room unit can cool quickly without removing enough humidity, reducing comfort and efficiency.
- Check the exact window or wall opening, sash type, mounting kit, electrical supply, plug and circuit, condensate path, airflow direction, and noise rating.
- Compare ENERGY STAR certified models using tested cooling capacity and efficiency, and consider a lower-global-warming-potential refrigerant when available.
- Air-seal the installation with the supplied materials, follow leveling and drainage instructions, and keep heat-producing devices away from the thermostat.
Common questions
Why does this calculator use a capacity table instead of BTU per square foot?
ENERGY STAR publishes stepped room-area bands with specified capacities rather than one universal BTU-per-square-foot rate. Using those bands preserves the source method. The listed adjustments then address shade, sun, regular occupants beyond two, and kitchen use without inventing a whole-house load model.
What ceiling-height factor should I enter?
Use 1.0 for the ENERGY STAR table’s eight-foot ceiling basis. The source advises considering more capacity for higher ceilings but does not publish one universal multiplier. Obtain a factor from product guidance or a qualified load assessment when ceiling height or room geometry is unusual.
Why can an oversized room air conditioner feel uncomfortable?
ENERGY STAR explains that an oversized unit may cool the room before removing enough humidity, leaving cool but damp or clammy air. Correct capacity, low-speed operation where available, proper installation, and suitable airflow help the unit manage both temperature and moisture.
Can this calculator size central air conditioning for my house?
No. It applies a published table intended for one room or window air conditioner. Central and whole-house systems require a property-specific cooling-load calculation that considers construction, windows, infiltration, ventilation, ducts, orientation, climate, internal gains, and other rooms rather than this simplified chart.
Sources and reference standards
- ENERGY STAR — Room Air Conditioner SizingPrimary EPA room-area capacity table based on an eight-foot ceiling, plus published shade, sun, occupancy, and kitchen adjustments.
- ENERGY STAR — 2024 Room Air Conditioner FactsheetPrimary EPA consumer guidance on proper room-air-conditioner sizing, installation, humidity, shade, sun, and kitchen adjustments.
Use this result in a complete project plan
Home energy cost planner
A home-energy plan should begin with measured kilowatt-hours and the tariff that actually prices them, not a national bill or a promised savings percentage. Appliance schedules, electric-vehicle charging, future electrification, solar production and outage loads answer different questions. This sequence keeps energy, power, time and money in their proper units while preserving the source of every assumption.
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