Portable Air Conditioners Suck (Hot Air Into Your House)

Are you thinking of a portable air conditioner? Don’t. Step back. Put your wallet away.

I can’t think of a better way to waste time, money and energy than buying a portable air conditioner – although there are a couple of exceptions that have their place.

Whether you call it a reverse cycle air conditioning or heat pump, refrigerative air conditioners share common traits, namely they need a decent supply of air to extract or reject heat.

If you’ve ever walked past a window rattler or the outdoor compressor unit of a split system, you’ll notice two things. Firstly they have a big fan which creates quite a breeze. Secondly, they’re usually noisy.

While we often point out that reverse cycle systems are the most efficient way to heat and cool your house with electricity, there are always exceptions.

So Why Are Portable Air Conditioners A Bad Idea?

We recently covered the spate of social media ads promoting tiny scam “air cooling” devices only available online, but even the devices they imitate – full sized portable air conditioners sold in store by major Australian retail chains  – are suspect.

Put simply, they’re expensive, inefficient, ineffective, noisy, and actively force your house to leak energy.

They won’t make you comfortable unless you sit right in front of the vent, where you have to listen to the machinery.

The main problem with portable air conditioners is this :

They take the air you’ve just paid money to condition;

and then blow it straight out the window.

Really the only good purpose they serve is to part fools with their money, which is unfortunate because I’ve seen first hand how heat stress wrecks a normally rational person’s purchasing decisions. Even a qualified scientist will buy one of these things when sleep deprived and sweltering through a heatwave.

These things suck.

How Is Reverse Cycle Supposed To Work?

There are two coils in any heat pump, one heats air up, the other cools air down, and they’re normally placed so that one is inside the house to create a pleasant atmosphere, while the other is outside to reject thermal discomfort.

Reverse cycle makes cool air cooler and hot air hotter, but doesn’t mix them.

A straight air conditioner cools the inside of your house while a reverse cycle unit will work both ways to provide home heating and cooling.

The only time both coils are in the same box is when you have an old style window rattler. These units were sometimes fitted through a house wall but they always one coil in the air outside, while the other coil was separated to condition the air inside.

Extraction Fans Aren’t Comfortable

Say you’re using it for summer – a portable reverse cycle system passes your interior air over the inside coil to make it nice and cool (plus condense some moisture that will need to be collected and emptied occationally).

However the outside coil is in the same box, so the machine sucks up your cool inside air, heats it up again and blows it outside. They work like a range hood or bathroom extraction fan, except they extract air you’ve just paid money to cool.

Portable air conditioning quite literally sucks. I’d ban them if I was king.

The Kicker Is Leaks

When you extract air from the room, to run through the coil which should be outside, then the uncomfortably hot air will be forced back into the room. Unconditioned air will leak from outside, through gaps, vents and doorways. Worst of all the exhaust pipe will undoubtedly leak where it goes out the window.

It’s just like your fridge – cool on the inside, warm on the outside, and pointless if you leave the door ajar.

Window air conditioners might leak a bit, but they’re not outright fraud like a portable unit.

Some Portable Options Make More Sense

There are models with two hoses, (or two in one) to separate the outside air stream from the inside one. They’re not such a flawed design.

What’s fundamentally better is a portable split system. They may still be noisy and even more cumbersome but on general principle that’s what I’d go looking for if I was stuck in a place needing it.

I’m not even sure these are available in Australia, but if you can chuck one half out the window and seal the opening with a towel it should work.

Don’t Confuse Evaporative Coolers

Colloquially known as a swamp box, a portable evaporative cooler is at least honest about its ability. At best, it’ll knock about 9 or 10ºC off the ambient temperature, but only works if you have low humidity to start with.

While it doesn’t sound like much, when temperatures drop to 20ºC you can really chill the place overnight and then close up the windows ready for the next day.

It’s basically a fan, a pump and some filter material, so they’re lightweight and cheap to buy. Unlike refrigeration, you need the windows and doors open so the air can flow through unimpeded, and that’s OK because they’re very cheap to run. All you need to do is keep the water reservoir full.

Trust Me, I’ve Tried

I’ve slept next to one of these noisy bastard things. I’ve even built a plywood duct, married up to an external window, to try and make it more effective. In temperature terms the experiment improved things from dismal to passable, but it was still too loud to be pleasant.

Sadly, it’s people who can’t afford a half decent split system installation that are likely to buy these things, proving yet again that it’s expensive being poor.

For an air conditioning solution that actually works, read our deep dive guide on reverse cycle systems.