It’s a reasonable question, and the honest answer is that these units aren’t built for it.
Rated capacity assumes one enclosed space
Every BTU and m² rating in this family — the Dreo AC318S’s sizing guidance, Temprium’s stated 20 m (66 ft)², Gymax’s 45 m (148 ft)² — assumes a single, reasonably enclosed room. Opening a door to a second room effectively increases the volume being cooled without any corresponding increase in capacity.
Cooled air doesn’t travel far on its own
Without ducting or forced circulation into a second space, cooled air mostly stays near the unit and dissipates through doorways rather than meaningfully cooling an adjacent room.
If two rooms genuinely need cooling
The more effective approach in this family is a correctly sized unit per room, or a single larger unit rated for the combined open-plan area if the rooms are already effectively one connected space — see our sizing guide for how to judge that.
What we would not do
Recommend an undersized single unit with doors propped open as a two-room solution. In practice this usually means both rooms are only partially cooled, and the unit runs constantly trying to reach a setpoint it can’t achieve across that much volume.
The questions that keep coming up
Would leaving doors open between rooms help?
Only marginally, and it works against the unit — an open door effectively increases the room volume the AC has to cool, without adding capacity. It usually results in neither room being properly cooled rather than both being adequately cooled.
Last reviewed 24 August 2026