Efficiency and hose setup
Single-hose portable ACs pull conditioned air from the room to exhaust heat — they fight themselves and use more kWh per BTU. Dual-hose models separate intake and exhaust — better, still less efficient than window units.
Window units mount half inside, half outside — heat leaves directly. Same BTU rating, window units usually cool faster and cheaper to run.
SACC vs ASHRAE ratings on the box
Portable ACs often print two BTU numbers. ASHRAE is lab-style; SACC (seasonally adjusted) is closer to real-room performance and is usually lower. Shop and size with SACC when both appear.
If a portable lists only ASHRAE, treat the effective cooling as lower than a same-BTU window unit — bump one retail step or prefer dual-hose.
When portable still makes sense
Size portables with the same room BTU math — then expect to buy a higher nominal BTU than a window unit for the same room. Start with the room AC calculator or window AC calculator.
- Rental leases banning window brackets
- HOA rules on visible window units
- Temporary cooling one season in a home office
- Rooms where drilling is impossible