It depends on how much you're prepared to pay. My wife and I live in S W England, and the summers can get very hot - like this year. We tried all different methods to keep cool, with little success. Fans simply move the warm air around the room; evaporative coolers don't work very well because the English air is always too damp for effective cooling; opening the windows worked reasonably well if you choose the time carefully, but you run the risk of letting in night flying insects; portable air conditioners are very noisy, and there's the problem of venting the hot air outside.

In the end, we opted for two fixed air con systems - one upstairs and one downstairs. Expensive to install, and can be expensive to run, however we also installed solar panels on the roof, which reduced the electricity costs to zero. They still need to be serviced every two years.

An advantage with fixed air con systems is that they can be run in reverse to give very cheap heating, but this works best in early spring and late autumn. For winter, we still have the gas central heating.

Shopping around local installers, you could probably get fixed air con systems installed for about 1200 pounds each. Servicing every two years costs around 70-100 per system. Solar panel systems start (I think) from about 6500 pounds, but you will get that money back with interest!