PortaCool Calculator

Portable AC calculator based on real cooling power

Portable air conditioners are labeled with two BTU numbers, and the big one on the box is not what you get in a real room. Move the sliders to find the SACC rating you need, whether a single or dual-hose model makes sense and what it will cost to run.

Sun exposure
Climate
Room use
Window and setup

SACC vs. ASHRAE: the two BTU numbers on every box

Until 2017, portable air conditioners were rated only with the ASHRAE 128 method, which measures cooling output in ideal lab conditions and ignores the heat the unit itself adds to the room. Because a portable AC sits inside the room, its warm exhaust hose and the outside air pulled in through gaps (to replace the air it blows out) reduce its real cooling effect a lot. The US Department of Energy therefore introduced the Seasonally Adjusted Cooling Capacity (SACC), which accounts for these losses.

For a single-hose unit, the SACC is often only 50–65% of the ASHRAE figure. A unit sold as “14,000 BTU” may deliver about 8,000–10,000 BTU SACC. Dual-hose units lose less because they draw cooling air from outside, so their SACC is typically 70–80% of ASHRAE. Always compare models by SACC – this calculator gives you the SACC you need and an approximate ASHRAE number so you can recognize the right boxes in a store.

How much SACC for my room?

Room sizeSACC needed (normal sun, 8 ft ceiling)Typical ASHRAE label
Up to 150 sq ft5,0008,000
150–250 sq ft6,00010,000
250–350 sq ft7,000–8,00012,000
350–450 sq ft9,000–10,00014,000
450–550 sq ft12,00014,000 dual-hose
550–700 sq ft14,00018,000 dual-hose or two units

Single-hose or dual-hose?

A single-hose portable AC uses room air to cool its condenser and blows that air outside. This creates slight negative pressure, so warm air from other rooms and outdoors leaks back in. It works well in small and medium rooms in moderate weather and is cheaper and lighter. A dual-hose unit pulls outdoor air through one hose to cool the condenser and returns it through the other. It cools faster, keeps working well on very hot days and is the better choice for rooms over about 400 sq ft, sunny rooms and hot climates. The calculator recommends dual-hose when the required SACC exceeds about 8,000 BTU or when conditions are hot.

Venting and placement

Keep the exhaust hose as short and straight as possible. Most hoses extend to 5–7 feet, and every extra foot and bend reduces efficiency and lets more heat radiate back into the room. Window kits typically cover openings from about 26 to 48 inches and can be used horizontally or vertically; extra panels or a cut-to-size board can cover wider windows. Seal all gaps around the kit with foam strips, and if possible insulate the hose with a fabric hose cover.

Humidity and drainage

Portable ACs also remove moisture. In humid climates, choose a unit with a separate dehumidifier mode and either self-evaporating technology (which sends most condensate out with the exhaust air) or a continuous drain hose. Otherwise you may need to empty the internal tank every few hours in sticky weather.

Noise

Because the compressor is inside the room, portable ACs are louder than window units or mini-splits. For a bedroom, look for 52 dB(A) or less on the low fan setting; inverter models can reach about 42–44 dB. Above 56 dB, most people find it hard to sleep.

Portable AC FAQ

What size portable AC do I need for a 400 sq ft room?

About 9,000–10,000 BTU SACC in normal conditions. That usually corresponds to a 14,000 BTU ASHRAE single-hose unit or a 12,000 BTU ASHRAE dual-hose unit.

Is a portable AC as good as a window AC?

No. With the same SACC rating they cool similarly, but portable ACs use more electricity for the same cooling and are louder. Their advantage is that they fit windows where a window unit cannot be installed and can be moved between rooms.

Can I vent a portable AC without a window?

It must vent outside somehow: through a wall port, a sliding door kit, a dryer vent or a drop ceiling into a vented space. Venting into an attic or another room simply moves the heat and does not work.

How much electricity does a portable AC use?

A typical 8,000 BTU SACC unit draws about 900–1,100 watts on high. Running it 8 hours a day costs roughly $1.20–$1.50 at $0.17/kWh.

Can I extend the exhaust hose?

Manufacturers generally advise against it. Longer hoses reduce airflow and cooling and may void the warranty. Move the unit closer to the window instead.

About PortaCool Calculator

PortaCool Calculator was created because the two BTU ratings on portable air conditioners confuse most buyers. This free tool converts your room details into the SACC capacity you actually need and explains the trade-offs between hose types, noise and running cost. We are independent and do not sell air conditioners.