Air conditioning

Air conditioning

On Wednesday Britain recorded its hottest July day ever, and with night-time temperatures remaining well above 20C across large parts of the country, it is no surprise that portable air conditioning units have been flying off the shelves.

Comet says is it selling an air conditioner every 30 seconds - other retailers say they have been selling 10 times as many as is normal. Some opportunistic retailers have even been caught upping prices by 30% in an attempt to cash in. A look in your local hardware store, or any big electrical outlet, shows there is no shortage of units to choose from - some from as little as £40. But are they any good, and how much do you have to pay?

What are they?

Many of the portable units you will see aren't air conditioning units, but air coolers. These work by using water to suck some of the heat out of a room. They are cheap, but according to Chris Michael, the boss of Guildford-based aircon retailer Meaco, few have much impact on a room when it's humid.

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He has been selling portable cooling units for 15 years and currently only sells one air-cooler costing £189, as he describes most of the cheaper models as "a waste of money".

Air coolers have the advantage of being much quieter than an air conditioner - they are also much cheaper to run at around 1p an hour, if not less.

There are no refrigerants - making them better for the environment - and they are easy to move around the house as there is no trailing hose. But Mr Michael's message is simple: "Buy a decent one, or be prepared to be disappointed."

Although slightly more sophisticated, air conditioning units are still very simple and operate in a similar way to a refrigerator. They have a compressor making them noisier - the air from the room is sucked in, passed over a cold coil and blown out again to provide a fresh feeling. Aircon units also remove some of the moisture that makes the air feel sticky.

Most push the heat out via a hose which needs to be put outside the room you are trying to cool - ideally out of a window that is sealed around the hose.

How do I tell a good one?

All air conditioning units carry a British Thermal Unit (BTU) rating that will be a good guide to how much cooling it will provide. Mr Michael says buyers should shun any machine with a BTU of much less than 10,000 as this is the minimum required to cool a room as small as a bedroom.

Larger rooms will need a 12,000 unit - offices and other larger spaces need 16,000. As a general rule of thumb, he says any machine costing less than £100 is not worth bothering with. He also suggests that some of the popular brands that have come into the market relatively recently should probably be avoided.

"The best units are made by companies few consumers have heard of - most notably Amcor and Prem-I-Air."

Other things to look for include portability, if you plan to move it around. Some are more unsightly than others, but fashion victims will be delighted to learn that silver metallic designer models are now available from £300.

What do they cost?

The cheapest portable air conditioning units at johnlewis.com start at £249, while at Meaco.com they start at £189, although most are in £250-£500 bracket. Prices can rise to as much as £850, but it really pays to shop around. Prices for the same model can vary by as much as £300. The website Froogle is a good starting place.

If you want to go for a large installed option, Mr Michael says these have improved dramatically in recent years - prices start at around £600.

The BTU rating also gives a good indication of its running costs. A 10,000 BTU machine costs 10p an hour to run - 12,000 units cost 12p and so on.

Although many will consider a decent night's sleep to be priceless, two machines running solidly for a week will cost £33.60 - not an inconsiderable sum.

If there is mass take-up of air conditioning it will have severe consequences for electricity consumption. The environmentally-conscious should stick to fans.

What else?

Mr Michael advises home owners to keep curtains and windows closed during the hot weather; open a loft hatch to allow hot air into the loft space. Those planning a cool sleep should run the conditioner in the day and turn it off before they go to sleep.

As well as cooling, many units also dehumidify and filter the atmosphere which can be beneficial for those with allergies. They can also greatly aid asthma sufferers, he says.

guardian.co.uk © Guardian News and Media 2009