Good temperature control is one of the most effective ways to improve the quality of your homebrew. It’s what elevates great beer above good beer. In fact, the ability to select and maintain the temperature of a fermentation is probably the single greatest technical advantage that professional brewers enjoy over homebrewers.
Good temperature control ensures that fermentation remains within the range of conditions best suited for your yeast of choice. This might be as high as 70–80°F (21–27°C) for Belgian ales or as low as 45–55°F (7–13°C) for German lagers. Here are a few ideas, roughly in order from least to most effective (and, correspondingly, least to most expensive) for keeping your cool.
Do Nothing
If you don’t mind brewing seasonally, then you can take advantage of your home’s natural temperature variations. You probably won’t be able to make lagers, but it should be fairly easy to brew British ales in winter and saisons in summer. This is how brewers did it before the advent of air conditioning, and many of us still brew this way at least some of the time.