Measure the space before reading product headlines
Measure the conditioned area in square feet and record ceiling height, connected open rooms, direct afternoon sun, regular occupants and heat-producing equipment. A listing that names only square footage cannot see those conditions.
Portable units also need a suitable window or opening for the exhaust arrangement. Measure the opening and route before treating any capacity as usable. A unit that cannot be installed according to its instructions is not correctly sized for the room, regardless of its headline BTU.
Use SACC with SACC
The DOE portable-air-conditioner test procedure defines seasonally adjusted cooling capacity, or SACC, in BTU per hour. The method accounts for specified test conditions and effects such as duct heat and infiltration. That is why a portable unit can display a lower SACC figure beside a higher ASHRAE figure.
Keep the two ratings in separate columns. There is no single conversion percentage that works for every portable model. If one candidate shows only ASHRAE capacity, find its matching SACC before comparing it with a model listed by SACC.
| Question | What to record |
|---|---|
| Room | Length × width, ceiling height and connected spaces |
| Heat conditions | Sun, occupants and heat-producing equipment |
| Cooling rating | SACC in BTU/h; ASHRAE in a separate column |
| Installation | Hose type, window-kit range and required clearances |
| Electricity | Input watts or annual kWh; never substitute BTU/h |
Treat a room-size chart as a starting point
ENERGY STAR publishes a square-foot-to-capacity chart for room air conditioners and adjustments for shade, sun, kitchens and occupancy. It is useful background, but portable ACs have their own SACC labeling and model-specific installation requirements. Do not silently transfer a window-unit capacity recommendation to a portable listing that uses another rating basis.
Use a chart to create a capacity range, then confirm the exact portable model’s SACC-based guidance. If the seller mixes ratings in one sentence, consult the manufacturer documentation and EnergyGuide information before buying.
Finish with fit, comfort and electricity
Capacity does not reveal operating cost. A 10,000 BTU/h SACC rating describes cooling output under the applicable test method; it is not 10,000 electrical watts. Use average input power or measured kWh with your schedule and electricity rate.
Compare only units that pass the room, opening and electrical checks. Then review drainage, filter access, sound evidence, storage and return conditions. This order prevents a low price or large ASHRAE number from winning before the appliance is shown to fit the job.
Choose your next step
Continue with the question that matches your next decision:
Sources & further reading
Numerical examples are illustrative unless explicitly described as measured. This guide does not claim hands-on product testing. Read the methodology and editorial disclosure.