Portable Air Conditioner Sizing

The number that matters on a portable unit is DOE's seasonally adjusted cooling capacity, in Btu per hour. A bigger figure on the carton is a different test.

Built by Jeremy Panasuk. Published October 3, 2026.

Quick answer: DOE's portable air conditioner test procedure reports seasonally adjusted cooling capacity (SACC) in Btu/h. For a single-speed unit, SACC weights the adjusted cooling capacity 0.2 at the 95°F condition and 0.8 at the 83°F condition. The adjusted capacity already subtracts heat the ducts and infiltration air put back into the room. Match a portable unit to your room using that SACC, not a larger marketing BTU, and not the window-unit row by itself.

Why a portable is not a window unit with wheels

DOE's Energy Saver 101 groups a portable air conditioner with a window unit as room air conditioning: spot cooling from one package. The package still has to reject heat. On a portable, that heat leaves through a duct in the window. DOE's test procedure, in the 2023 portable AC test-procedure notice and in 10 CFR Appendix CC, treats that duct as part of the measurement. Adjusted cooling capacity is the measured indoor cooling, adjusted for duct heat transfer and for infiltration air. SACC is then the seasonally weighted combination of those adjusted values.

Appendix CC writes the single-speed case as SACC = ACC at 95°F × 0.2 + ACC at 83°F × 0.8, with separate forms for single-duct and dual-duct units. The 0.2 is the weighting factor for the 95°F test. The 0.8 is the weighting factor for the 83°F test. Variable-speed units use the 95°F result and the low-speed 83°F result in that same 0.2 / 0.8 split. There is also a full-load SACC that uses full compressor speed at 83°F. None of those equations is "take the number on the front of the box and multiply by 0.7." DOE does not publish one conversion percentage from a marketing BTU to SACC. If a carton shows two capacities, the one labeled SACC is the one this test procedure defines.

The ENERGY STAR room air conditioner chart is still the right shopping table for a window or through-the-wall room unit: floor area in, BTU/hr out, 8-foot ceiling, then shade, sun, extra people, and kitchen. DOE's FEMP room-air-conditioner page, updated December 2024, says that purchasing guidance applies to casement, through-the-wall, and reverse-cycle room air conditioners, and that portable air conditioners are among the products excluded from it. Use the chart to understand the room. Do not paste a portable's marketing BTU onto a chart row and call it sized.

Affiliate

Affiliate disclosure: as an Amazon Associate, we earn from qualifying purchases — at no cost to you. Check the model's published SACC before you buy. A search result is not a capacity rating.

Portable air conditioners on Amazon

Worked example: 250 sq ft, then read SACC

Start with the room, using this site's room-load function so you have a planning rate in BTU/hr. Inputs: 250 sq ft, 8 ft ceiling, 2 windows, average sun (factor 1.00), average insulation (factor 1.00).

Shell = 250 × 25 = 6,250 BTU/hr. Windows = 2 × 600 = 1,200. Subtotal = 7,450. Raw load = 7,450 × 1.10 = 8,195 BTU/hr. Rounded up to the next 500, the planning result is 8,500 BTU/hr.

ENERGY STAR's chart puts 250 up to 300 sq ft at 7,000 BTU/hr for a room air conditioner, before sun, shade, people, or a kitchen. Same floor area, two published answers, because the chart does not add this calculator's window term or its 10% margin. If you were buying a window unit you would start at 7,000 and apply only the chart's own adjustments. If you are buying a portable, neither 7,000 nor 8,500 is a SACC. They are targets you compare with the model's SACC. A portable whose carton leads with 10,000 or 12,000 BTU and whose SACC is a smaller tested number has already had duct heat and infiltration subtracted inside DOE's procedure. Buying the larger figure because it "clears" 8,500 can put an oversized machine in the room. ENERGY STAR's oversize warning still applies to the cooling you feel: a unit that is too large cools the space before it removes the humidity.

This page will not convert 8,500 into a fake SACC. The test is per model. Open the spec sheet, find SACC in Btu/h, and compare that single number with the planning rate and with the ENERGY STAR row for the floor area. If the sheet does not state SACC, you do not yet have the DOE capacity.

Common mistake

Sizing the portable as if the hose were free. The hose is why DOE adjusts the measured capacity before it publishes SACC. The matching mistake is a fixed discount — "SACC is always 70 percent of the big number" — which Appendix CC does not say. Dual-duct and single-duct units are calculated separately in that appendix. A dual-duct chassis is not automatically the single-duct formula with a second hose drawn on the carton. Read the configuration the test used.

Limits, and when to call a pro

SACC is a product rating. This calculator's 8,500 BTU/hr is a room planning figure from a rule of thumb. Neither is ACCA Manual J, and DOE's heating and cooling guide says to insist on Manual J for heating and cooling equipment because square-foot rules skip climate and the envelope. A portable is a poor substitute for a central system that needs that calculation. If the room is a whole apartment, or the ceiling is well above the 8 ft the ENERGY STAR chart assumes, stop and use the calculator only as a first pass, then a contractor for a real load. Window-unit rows for nearby floor areas are on the 250 sq ft and 300 sq ft pages. They are not portable SACC tables.

Compiled with AI assistance from the sources below. Spot an error? Email jpanasuk@gmail.com.

Sources

10 CFR Appendix CC to Subpart B of Part 430, portable air conditioner test method — https://www.ecfr.gov/current/title-10/chapter-II/subchapter-D/part-430/subpart-B/appendix-Appendix%20CC%20to%20Subpart%20B%20of%20Part%20430 — accessed Oct 3, 2026.
U.S. Department of Energy, Energy Conservation Program: Test Procedure for Portable Air Conditioners (May 2023) — https://www.energy.gov/sites/default/files/2023-05/pac-tp-fr.pdf — accessed Oct 3, 2026.
U.S. Department of Energy, FEMP purchasing guidance for room air conditioners — https://www.energy.gov/cmei/femp/purchasing-energy-efficient-room-air-conditioners — accessed Oct 3, 2026.
ENERGY STAR, Room Air Conditioners — https://www.energystar.gov/products/room_air_conditioners — accessed Oct 3, 2026.
U.S. Department of Energy, Energy Saver 101: Home Cooling — https://www.energy.gov/sites/default/files/2016/11/f34/HomeCooling101.pdf — accessed Oct 3, 2026.
U.S. Department of Energy, Guide to Home Heating and Cooling (DOE/EE-0338) — https://www.energy.gov/sites/prod/files/guide_to_home_heating_cooling.pdf — accessed Oct 3, 2026.

Frequently asked questions

What BTU number should I use for a portable air conditioner?

Use the seasonally adjusted cooling capacity, SACC, in Btu/h. DOE's portable-air-conditioner test procedure defines SACC as a weighted average of adjusted cooling capacity at 95°F and 83°F, and the adjusted capacity already accounts for duct heat and infiltration air.

Does the ENERGY STAR window chart apply to portable units?

The ENERGY STAR room air conditioner chart is the shopping table for room air conditioners sized by floor area. DOE's FEMP room-air-conditioner purchasing guidance excludes portable air conditioners from that guidance. Do not treat a portable marketing BTU as if it were a row on the window chart.

Is there one percentage that turns a marketing BTU into SACC?

No percentage like that appears in DOE's SACC definition. SACC is calculated for the model from test data. Read the model's published SACC instead of converting a larger number by a rule of thumb.