Do a manual J for the rooms that the Room AC is supposed to cool.

How much area you can cool with a Room AC varies due to a lot of factors.

I am a Retired HVAC Contractor & Tech, I cool perfectly over 850-SF in 104 heat Index, with a Half-Ton 6,000-Btu/hr Room AC, that footage is the entire first floor of my 1937 Farm home that is loaded with windows with little shade.

I cool the upstairs bedroom, hallway, stairwell & bathroom, "usually only during the evening," with a Room AC & circulating fans.

Click the anchor links to get directly to the Room AC performance & how I make it work with two 20" circulating fans. "Air circulation is a KEY factor" in how much area a Room AC will cool. Disclaimer: Use your own judgment, NOT mine. udarrell

Here is a link that might be useful: HALF TON ROOM AC COOLS OVER 850 SF

I don't quite understand how such a small unit can cool that much space. MANY YEARS ago I had a small 5,000 BTU window unit in an upstairs room which BARELY took the heat off a 10 x 10 room with low ceilings.