This is a real, if often overlooked, efficiency question that affects every single-hose unit in this family — which is all of them we’ve reviewed so far.
What a single hose actually does
A single-hose portable AC exhausts warm air outside through one hose, and as it does, it pulls replacement air in from wherever it can — cracks around doors, corridors, the room next door — creating negative pressure the unit then has to cool along with everything else.
Why a well-sealed installation matters more here
Because every unit in this family is single-hose, sealing the window kit properly is the main lever available to reduce this penalty. A poorly sealed kit both lets warm air back in directly and increases how much replacement air gets pulled from elsewhere.
Dual-hose units avoid this, at a cost
A dual-hose design draws its intake air from outside as well, avoiding the negative-pressure effect — genuinely more efficient, but larger and typically pricier. None of the units we’ve reviewed on this site use this design.
What we would not do
Assume a single-hose unit’s real-world performance will match its rated BTU figure regardless of installation. A well-sealed single-hose unit performs close to spec; a poorly sealed one loses a real, if hard-to-quantify, share of its rated capacity.
The questions that keep coming up
Why do most portable ACs use a single hose despite the downside?
Cost and footprint, mainly — a dual-hose design needs a second intake path and is generally larger. Every unit we've reviewed in this family, including the Dreo AC318S, is single-hose, which is representative of most of the market at these price points.
Last reviewed 24 August 2026