With the UK getting warmer, portable air conditioner sales are going through the roof. In particular, sales increase after a few days in a row of hot weather, a phenomenon that’s likely to increase every year.
It seems as though people can stick out a hot night or two, but that’s the limit. When even the best fans can’t cut it anymore, people turn to portable AC. That’s certainly what I did, after having a loft conversion.
Moving up into the roof space has been great in terms of the space, but with a south-facing front and hot air from the rest of the house moving upstairs, the loft space can become unbearable on a moderately warm day; in a full-on heatwave, it’s just horrible being upstairs.
After testing and reviewing multiple portable AC units in my house, I’ve concluded that portable AC is better than a fan, but only if it’s used properly. Here’s what I’ve learned.
Cooling capacity is very important
Air conditioning units are rated by cooling capacity in British Thermal Units (BTUs). The higher the capacity, the greater the cooling capacity. Higher cooling capacity is required for two reasons: one is to deal with a larger space, and the second is to cope with the amount of heat.
You also need to account for the level of insulation: properly insulated homes keep out the heat and retain the cold better than poorly insulated homes.
All of this can make life rather complicated, but you can use the BTU Calculator as a guide for what size AC you need.
That said, I tend to find that a minimum of 10,000BTUs is about right for most rooms in a typical house, and 12,000+ will do better in most bedrooms. I’d avoid the cheaper, lower output models (8000BTUs and below).
You need to sort out the ducting properly
All portable AC units need to be ducted out of a window. Air conditioning works by extracting heat from the air in a room and pushing it outside via the duct. With a window open, hot air can easily come into the house, so it’s best to have a proper window seal. Most AC units will come with plastic slide that will fit at the bottom of a sash window, but if you’ve got casement windows (they open outwards on hinges), you’ll need a fabric kit that sticks on, or you can have a custom plastic insert made (there are plenty of sellers on eBay that will do this, such as this window seal kit).
The requirement for the duct means that you can’t always place a portable AC unit where you want it. If you’ve got a hot lounge with a conservatory attached to it and no external doors or windows, you won’t get your AC working.
Having to place the AC unit near a window isn’t always ideal, so you may need to plan to rearrange your furniture.
Don’t expect it to be icy cold, certainly not fast
Due to the way that AC works, there’s a limit to how much a portable unit can do, regardless of its maximum cooling capacity. With a properly installed split AC, which is way more efficient, turning it on in a hot room can have everything cooled down quickly to the point where it can even feel cold.
With portable AC, I find that it takes a lot longer, particularly in very hot rooms, such as my loft. Turning the AC on as I come up to bed is no good; instead, I need a good two hours before bedtime to get the temperature down to something reasonable (around 24°C) on a very hot day; possibly even longer.
A temperature of 18°C is hard to reach on the hottest days, so I focus on setting the AC to a level where it’s easy to sleep. For me, 23°C is a good target, as it’s cool enough to sleep in and reduces how much power the AC unit uses.
Get used to the sound
On a warm evening, turning the AC on two or three hours before bed is usually good enough to lower the temperature far enough. And, as long as it’s cool outside, I then turn the AC off and open the windows to maintain a comfortable temperature.
On the hottest of nights, as soon as the AC turns off, the room temperature ticks upwards, and I have to have the air conditioning unit on all night. Even the ‘quiet’ portable air conditioning units are far from this. With the compressor turned on, they rumble loudly through the night.
There’s not much you can do about the noise, except set the AC to a temperature that’s easy to maintain, so that there are extended periods when the compressor is off, reducing noise. It’s not perfect and properly intalled split AC is quieter and more efficient, but it’s a lot more expensive and can’t be fitted to every house.
You need somewhere to store them in winter
Portable AC units are all relatively big and bulky. The larger, more powerful ones aren’t far off the size of a fridge. While they have wheels to make moving them around a room easy, they’re a lump to take up and down stairs.
In winter, when you don’t need them out, they should be drained of any excess water (accumulated while running), and then stored. Ideally, an AC unit should be stored upright and in a dry place, such as a cupboard or garage; you should avoid storing them in damp, cold places, such as sheds.
You shouldn’t lay a portable AC unit on its side, as it can cause damage to the compressor or cause the refrigerant to shift. If an AC unit does have to be transported on its side, then stand it upright for 24 hours to allow fluids to resettle before using it.
All of these requirements do need to be considered before you buy.
Are portable AC units worth it?
Despite the drawbacks, portable AC units are relatively good value and, unlike a fan, will actually cool a room down, provide they have a large enough cooling capacity and they are vented properly. In my hot loft room, my portable AC unit makes the long periods of high heat tolerable, and I wouldn’t be without it.
