Here’s Consumer Reports top 8.

A portable may be the only workable choice but they aren't efficient compared to a window or through-the-wall unit. Portables have all of the mechanism within the room, which adds heat to the room from the compressor operation. A two-hose portable is better than a single-hose portable in that respect. Single-hose actively exhausts cooled room air through the unit to disperse the compressor/condenser heat to the outdoors. A double-hose pulls outdoor air in, through a separate path, across the compressor/condensor and blows it back outdoors, which is less detrimental to cooling the room.

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Whatever model you choose, be sure to buy an insulation kit to cover the hose. It makes a huge difference.

We tried a portable unit in an upstairs bedroom a few summers ago, and a couple of things made a real difference for us. First, a dual-hose model cooled much more evenly than the single-hose one we had before, because it was not pulling warm air in from the rest of the house as it ran. The hose insulation tip above is a good one too, since that hose gets surprisingly warm and can work against you if it is just sitting in the room. It is also worth checking the drain setup before you buy, especially upstairs. Ours needed the tank emptied often on humid days, so a model that could drain continuously to a sink or out a window would have been much easier to live with. For sizing, I would measure the room and check the rating for that square footage rather than going by the room type alone, and keep the doors closed while it runs so it is not trying to cool the hallway as well. It will not be as efficient as a fixed unit, but with the right hose setup and a realistic room size it can make an upstairs room comfortable on hot evenings.

I run Ocala Pro AC Repair here in Ocala, FL — we see this a lot in Florida heat, and upstairs rooms are usually the hardest to keep cool.

A portable unit can help a single room, but it is worth knowing its limits before you buy. Most single-hose models push cooled air into the room while pulling warm air in from elsewhere in the house to replace the air they exhaust, so they often struggle upstairs where heat already collects. A dual-hose model is usually the better choice for a bedroom because it draws outside air for cooling the condenser and does not create the same negative pressure.

When comparing models, look at the SACC rating rather than the headline BTU figure, as that is the more realistic measure of cooling capacity. Choose a size matched to the room, and check that it is Energy Star certified, has a washable filter you can clean easily, and a condensate system that suits how you will use it — some need regular draining in humid conditions.

You can also help any portable unit work better: keep the exhaust hose as short and straight as possible, seal gaps around the window kit, close the bedroom door, block direct sun during the afternoon, and clean the filter regularly. If the room still stays warm, the problem may not be the portable unit at all.

If your main system leaves the whole upstairs warm, or the room cools only when the door is open, it is worth having a professional check airflow, ductwork, insulation and return air. In some older homes, a small ductless mini-split for that bedroom ends up working far better than a larger portable unit.