When a heat wave strikes, air-conditioning starts to look more and more essential. If your home or living space can accommodate it, a window air conditioner will always be a powerful and affordable way to cool down a room. But they won't work for every home. Maybe your only window is a fire escape, and you can't block it with an AC unit. Maybe you don't have a standard double-hung window. That's where portable air conditioners come in. These have historically delivered poor results—they often don't cool a room as well and are really noisy—but they're getting better every year.

The versatile EcoFlow Wave 2 is far more expensive than most window AC units, but it has some serious cooling muscle for a portable air conditioner, and it can even double as a heater when winter rolls around. I have been using it to cool my office during the day and then carrying it upstairs to chill my bedroom at night, and it has made life more bearable as temperatures soar.

The EcoFlow Wave 2 is a compact AC unit that weighs 32 pounds. It's rated at 5,100 British thermal Units (BTU) for cooling and 6,100 BTU for heating, and works best for rooms up to 107 square feet in size. The angular design measures roughly 20 x 12 x 13 inches. There are intake vents on the front and back, an exhaust vent on the top rear, and cool air (warm in heating mode) flows out the top vent at the front. EcoFlow supplies two ducts in the box—you must attach one to the exhaust vent at a minimum, or the unit will pump warm air back into the room.

Ideally, you'd have an exhaust vent and an intake vent going out the window, and EcoFlow provides a rectangular vent board with two holes for this purpose. The design also allows a single duct to be attached to the top front vent to pump cool air into a room or tent. That way, you can put the Wave 2 outside to reduce noise, though this would render the temperature sensor useless, because it would measure the outside temperature instead of your tent.

The bright LCD on top shows the current and target temperature. You can also see the remaining battery life when you have the optional add-on battery attached. There’s a big power button on the right and a button to cycle between cooling, heating, and fans on the left. There are also four buttons under the display to cycle between Max, Night, Standard, and Eco modes, to set the target temperature up or down, and to control fan speed.

As for charging, the permanently attached plug slots into any AC outlet, and there is an XT60 port for connecting solar panels and an XT150 for connecting the add-on battery. EcoFlow sent me the version with the battery. It slots securely into place under the Wave 2, and there is a small connector cable. Once attached, it feels like a part of the Wave 2. They won't come apart accidentally, and the battery adds a handle to the back that makes for easier carrying, though the two combined are heavy at almost 50 pounds.

The battery stores 1,159 watt-hours, enough for using the Wave 2 for two to three hours at max output, a little longer in Standard mode, and up to eight hours in Eco mode. It can act as a portable charger with a USB-A port capable of delivering up to 18 watts and a USB-C that goes up to 100 watts. The battery is essential if you plan to take the EcoFlow Wave 2 camping or anywhere without outlets. It is also rated for dust and water resistance at IP65, though the Wave 2 itself only has an IPX4 rating, meaning it can withstand splashes but is not waterproof, so you need to be careful using it outside.

My small office is south-facing, so having the EcoFlow Wave 2 chill it down during the day has been lovely. I wedged a single duct to vent the warm air out of the window. It took the temperature from 84 to 70 degrees Fahrenheit within an hour in Standard mode. My south-facing bedroom took longer to cool at night, because it is twice the size of my office. The vent cutout isn’t much use to me, as my windows open out with a hinge, but even just wedging the duct in there and closing blinds or curtains around it is enough for effective cooling.

The cooling mode draws up to 550 watts from the mains or 459 watts from the battery. Much depends on how warm the room is and your target temperature. It mostly hovered around 400 watts in the standard mode, and I measured sound at around 50 decibels. Crank it up to max and it cools far quicker, but it also gets a bit noisier, up to 60 decibels at the loudest. Using the Eco or Sleep mode draws less power and makes less noise. It hovers closer to 300 watts and around 40 decibels, and the battery keeps it running for up to eight hours. I had no trouble snoozing with it on, but I prefer some low-level noise (usually rain sounds) when I sleep.

You can also use the EcoFlow Wave 2 as a heater, but it will draw up to 600 watts from an outlet or 540 watts from the battery, so it's not cheap to run. There is also a fan mode that only seems to draw up to 40 watts, but it just creates a gentle breeze and doesn’t actually cool the air. Still, it allows you to extend the battery life by cycling between cooling and the fan.

The EcoFlow Wave 2 uses R290, a natural pure propane refrigerant with a low environmental impact and no risk of damaging the ozone layer. While you can hook up solar panels, you will need at least 400 watts of them and good conditions to run the Wave 2.

Since I've been testing portable power stations, I have been charging units like the Jackery Explorer 2000 Plus and EcoFlow’s own River 2 Pro with solar panels and using them to run the EcoFlow Wave 2 and charge its battery for free, eco-friendly AC. Zero guilt here!

To charge the battery, you need to plug in the EcoFlow Wave 2. If the AC unit is off, the battery will draw 700 watts and recharge in around three hours. Turn the EcoFlow Wave 2 on, and it will run normally, but the battery charges more slowly. One slight annoyance is that you can only charge it when it's connected to the Wave 2. But, aside from the ability to go off-grid, the battery also affords you some flexibility about how and when you charge up and how expensive the Wave 2 will be to run. That makes it well worth considering.

You need the EcoFlow app for firmware updates, and you can connect via Bluetooth, but hooking the EcoFlow Wave 2 up to Wi-Fi allows you to remote-control it from anywhere. It only supports 2.4-GHz Wi-Fi, though. The app offers all the same controls as the physical buttons and a few extras, like a timer function. You can also customize the ambient lighting and turn the annoying beep off.

There’s a drain-free function, so excess water should evaporate. You can also see an indicator on the LCD showing the water level, and EcoFlow supplies a wee pipe for draining it manually. I did spill some water when I moved it up the stairs one night, so you need to be careful about tilting when you carry it to avoid getting soaked.

The EcoFlow app is generally slick, but I have had to install three firmware updates for the Wave 2 in the two months I’ve had it. At one point, it refused to turn on, even with the battery charged and connected, though it still worked from the mains. I was on the verge of contacting support when a firmware update popped up and got it working again.

It's an effective AC unit that’s genuinely portable and works well in small enclosed spaces, provided you set up the exhaust duct. But it is very expensive. If you only need AC in a room or two, save your cash and pick from our Best Window ACs guide. If portability is a must, and you can afford it, then the versatile Wave 2 should be on your short list.