If you're anything like me then you'll be looking at the extremely high temperature forecasts and wondering, "Can I afford to cool down?"

Thanks to soaring electricity costs and the potentially-enormous power drain of cooling equipment, few people can happily leave aircon running 24/7. This is especially true for those renters who must rely upon portable devices.

So what are the costs? I've tested several units ranging from old fans, through the latest Dysons to a large portable air conditioner. The costs may be reassuring or terrifying. I'll also be looking at an often-overlooked factor - noise - something which needs to be considered before any purchase.

The following haven't been measured 100 per cent scientifically but the results will give you an idea of what to expect.

A Belkin Conserve Insight ($30ish) was used to measure power and the cost of that power. A price of 22c per KiloWatt Hour was used as it reflects current consumer electricity costs.

Desk fan ($30ish)

This old, bog-standard 30cm desk fan has three speeds and oscillates.

Low speed: 35W | $5 per month | $66 per year

High speed: 41W | $6 per month | $76 per year

This is never going to cool a room down, but if you're right in front of it, then the breeze will be most welcome. At low speed, it's relatively unobtrusive, emanating a roughly 40-decibel purr. At top speed it can hit 80 decibels depending on how close you are but it functions well if you're desperate. However, once a room is irredeemably hot, it will be blowing hot air at you and be of little help.

Still, if it's left on 24/7 for a month, a cost of $5 won't break the bank. Similar models can be had for around $30.

40cm floor fan ($30ish)

Floor fans should be more powerful, but basic models like this are still no good for cooling an entire room. Nonetheless, if you don't want a desk fan blaring in your face, then having this at your feet can provide welcome respite from the heat. It too has three power settings plus a rotating directional plate feature.

Low power: 47W | $7 per month | $90 per year

High power: 60W | $10 per month | $115 per year

At low power, it's borderline pointless, although it is very quiet at 45 decibels. However, it does offer some up-close cooling prowess at high power and isn't very loud at 56 decibels. It's not as powerful as the desk fan though.

Dyson Air Multiplier Blade-less desk fan ($300ish)

When this was tested in my office, it stopped everyone in its tracks thanks to its looks. However, it also stopped many people nearby working thanks to the loud, high-pitched noise it gives off. It's also disappointingly weak at pumping out cool air.

Low power: 10W | $2 per month | $19 per year

High power: 32W | $5 per month | $62 per year

Dyson makes a great deal about the lack of 'Buffeting' that its bladeless fans offer (buffeting is the rhythmic, uneven airflow produced from regular fans). Frankly, I never knew this was a problem until Dyson told me. However, they do have a point in that these fans are far far easier to clean than traditional models.

Ultimately, though, this costs ten times a regular fan and only offers only similar cooling performance.

Dyson Hot+Cold Fan Heater ($420ish)

If you want state-of-the-art then this is it. Dyson's Hot+Cold also acts as a heater which is handy for warming a cold room in winter months. In summer it's a bladeless fan and offers a design that would grace the smartest of homes (or at least those without climate control).

Low power: 9W | $2 per month | $17 per year

High power: 18W | $3 per month | $35 per year

It's far less intrusive than its fan-only sibling in that it doesn't have the same, loud, high-pitched whine - more of a general swoosh. A ten-level speed setting sees the decibels fluctuate from around 55 to 70.

It's power efficient but it offers no better cooling performance than a regular desk fan. Still, it's worth considering if you also get cold in winter.

Portable Air Conditioner ($300ish)

This large machine is hardly a model of efficiency, but it's the only type of product with the grunt to cool an entire room on a very hot day. According to my top scientific measuring device (baby monitor) it cooled a 3m square bedroom down by two degrees in 30 minutes. In truth it felt much cooler than before it was turned on and this has likely got something to do with the natural reduction of humidity that air conditioners provide.

Fan only mode : 73W | $12 per month | $140 per year

Air conditioner mode: 1025W | $162 per month | $1970 per year

Normal air conditioners have the most noisy part of the machine based outside of the home (for your neighbours to enjoy) but portable units have both the cooling technology and the exhaust system built into one machine. Not surprisingly it gets very loud and registered 90 decibels up close and 56 decibels from across the room. It was a struggle watching TV with it turned on.

Leaving it in fan mode is near pointless as it simply becomes a ridiculously-large-but-powerful desk fan.

The large exhaust pipe gets very warm after a while and naturally counteracts some of the cooling work being done. However, the exhaust does feed out of your window (assuming you have sash windows or at least windows that slide upwards). This may be a security concern for some though. Also note its size - it's both bulky and heavy. It will dominate a small room in every way.

In reality, despite the loudness, it's less intrusive than horrendous heat and humidity. You wouldn't leave it on constantly all year, and although it's expensive to run, leaving it on for an hour at a time can make a world of difference to a room in your home. Don't expect it to cool more than one room at once though.

This model comes from Kogan but it isn't the latest model (which can also act as a heater). Nonetheless, it has similar(ish) power usage and is generally similar to other portable air conditioners.

Portable units like this will likely get more efficient as the price rises, but bargain units like the Kogan cost just $300. A selection can be seen here.

Overall

My favourite small fan is the Dyson Hot+Cold, but then I have fond memories of it warming cold rooms over winter. For most people, regular desk fans are much cheaper and still very affordable to constantly leave running - at around $10 per month.

However, once a room gets irredeemably hot no fan will make any difference. As such, a bargain basement portable air conditioner can be a great buy at $300. Just remember that they can be incredibly intrusive in terms of noise and size and be sure you have a usable window to cope with the hot exhaust air. To keep running costs down, try and leave them running for an hour at a time.