How much does it cost to run a portable air conditioner?

A portable air conditioner is a good way to cool down a room, and they’re flexible, too, so you can move them around your house to get cooling where you want. But, you’ve probably heard horror stories about how much they cost to run.

Are portable AC units power hogs that shouldn’t be used, or can they be used efficiently to cool your home adequately? Read on to find out.

Input vs output running costs

As explained in our guide to how portable air conditioners work, these devices draw hot air out of your home. They work similarly to a fridge, using a compressor, which is why these devices use much more power-hungry than a fan.

It’s important to distinguish between the input power (how much electricity they consume) and the cooling power (how much they cool by). These figures can both be found in kW.

For example, the De’Longhi Pinguino 100 draws 700W of power but has a cooling capacity of 2.5kW. That means that its energy efficiency ratio (EER) of input to output is 3.57.

In comparison, the MeacoCool MC Series Pro 9000 BTU Portable Air Conditioner has a similar cooling power (2.6kW) but it draws 1kW of power, making it less efficient with an EER of 2.6 (about average for a portable AC unit).

When working out running costs, it’s the input power that we care about, as this tells us how much electricity is consumed.

So, how much does a portable AC unit really cost to run?

To work out running costs, you need to work out the kilowatt-hour figure (kWH) figure. That is calculated by multiplying the power consumption in kW by the number of hours that a device is on for.

So, take the De’Longhi Pinguino 100’s 700W power figure, and cover that to kW by dividing by 1000. That gives us 0.7kW. Multiply that by one hour and we have 0.7kWh for an hour’s use.

With the MeacoCool, it uses 1kW of power, or over an hour, 1kWh. 

Assuming the current price cap of 29.04p, the Pinguino 100 costs 20.33p per hour to run, and the MeacoCool costs 29.04p per hour to run.

The question is, how long does a portable AC unit need to be on for? The answer to that is more complex, as it depends on the current room temperature, outside temperature and the target temperature you want to reach.

The latter is particularly important, as once the AC unit hits its target temperature, it shuts down the compressor, so only draws a small amount of power; the compressor comes back to life when cooling capacity is required again.

To save money, it’s worth setting as high a target temperature as you’re comfortable with. Typically between 21°C and 24°C is a good target; go lower, and the AC unit won’t be able to cool to your target level, and it will keep running permanently.

On average, across the units that we’ve tested, it takes around two hours to hit a reasonable target temperature when used at night, with no sunlight to keep heating the building.

Given our two example units, that’s somewhere between 46.66p and 58.08p for the initial cooling job. At this point, the compressor will turn on and off as required as long as the AC unit is turned on and running.

If you sleep with the portable AC unit on, say eight hours after choosing pre-cooling a room, then how much power it uses again depends on how quickly the room heats up again, and the target temperature.

Working on averages, if the AC unit were to run for between 25% and 50% of that remaining time, you’re looking at a cost of between 40.65p and 81.31p for the Pinguino 100; the MeacoCool would cost between 58.08p and 116.16p. Those costs are for the night, and in addition to the initial cooling cost.

You can get some portable AC units that have an inverter, such as the De’Longhi Pinguino GentleJet Inverter. Using an inverter, the compressor speed can be adjusted to deal with the actual cooling demand. In other words, when the target temperature is close, the compressor can slow down, reducing energy consumption.

Although the nominal input power is 1kW (29.04p per hour), when the GentleJet approaches its target temperature, we saw power reduce to 465W (13.5p per hour). There are a lot of variables to consider, and the outside and inside temperatures, target temperature and size of room will all have an influence on how hard the AC has to work and, therefore, how much power it uses.

Working on some averages, pre-cooling a room and then turning the AC off and relying on open windows and a fan, will probably cost you between 46.66p and 58.08p, depending on the model and target temperature.

Pre-cool the room and run the AC all night (eight hours), and you’re looking at between 87.31p and 174.24p.

Run the AC all day and you’ll see costs go higher, so it’s best to target cooling at more opportune moments and minimise how much you use such a device to save costs.

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