Air Conditioners do's and don'ts: When you have young children, or are looking after the elderly, an air conditioner will be your weapon of last resort to beat the heat this summer. Here is what you need to do to make sure you get value for money.

The first rule of buying an air conditioning unit is to not wait until it gets hot! Air Conditioners sell out fast when you need them most, and chances are that by the time you get your hand on a unit, temperatures will have come down.

The second rule is that even a good air conditioner will use quite a bit of electricity, so make sure that you are getting the best deal on your energy at home before you buy! You could save up to £170 from switching your supplier, even if you have switched before - and these savings could pay towards buying and running air conditioning unit to keep you cool in the summer.

To figure out which air conditioning unit is most efficient for your property you need to give yourself time. You don't want to get stuck with an overpriced and inadequate no-brand air conditioner from your local hardware store, simply because everything else was sold out on the hottest day of the year...

Here are some simple pointers to getting value for money:

Type: Mobile air conditioners come in two types - 'integrated' or 'split' units.

• Integrated units work by housing the compressor unit (the bit that pumps the heat out of the air) inside the main control unit. This makes the unit more compact, and easier to move from room to room. On the downside, integrated units can be irritatingly noisy and tend to have less power, but they do cost less, with a decent unit priced around the £300 mark.
• Split air conditioners house the noisy bits in an external box, which you will have to find space for outside your window (they usually fit in the window box, and come with fittings). The outside unit is attached to the inside control unit by a thin pipe. This has the advantage of keeping the noise down. However, if you want to move your air conditioner from room to room, you need to consider that half of it sits outside. Split mobile units are also a bit more expensive, typically starting at £400.

Size: Buy an air conditioner with a cooling capacity that matches your property. Measure the room you wish to cool, and make sure that it corresponds with the stated capacity of the unit. An underpowered unit will have to run constantly without providing enough cooling, while an overly powerful machine will fail to remove enough moisture from the air and make the air feel clammy.

Noise: Air conditioners can be noisy. If you cannot demo a unit, ask for its noise performance in decibel - this is particularly important if you are buying an integrated unit. 36 to 40 decibel is considered a good performance. Noise is an important consideration if you wish to place the device in a bedroom.

Maintenance: All filters, air intakes, grilles and radiators need to be kept unblocked and clean at all times to maintain peak performance. Check that your unit allows easy access to all maintainable parts.

Usage: Most new units have a timer facility - before you leave your home, you can set the timer to start the machine 30 minutes before your return. You will enter into a nicely cooled home without wasting energy by letting the device run in your absence. Don't make your home too cold - set the temperature to around 24 Celsius for a comfortable environment.

Use a fan: Circulate the cold air with an extra standard fan to ensure efficient temperature distribution.

Make sure that you buy the most efficient unit - in the longer term an inefficient cheaper unit could cost you more than the slightly more expensive air conditioner that uses less energy or makes less noise.