Proper air circulation is essential for Space Buckets (and every other kind of indoor garden). Your bucket needs good ventilation to extract the heat from the CFL bulbs (or LED lights), and also to give the plant breaths of fresh air and plenty of CO2. In this section we review good ventilation solutions that you can use for cooling your always trusty bucket garden.
110/220v fans These fans are a step up from standard PC fans, as they run at line voltage (110v or 220v, depending on where you live). This cooling solution is sturdy and reliable, protected with a metal frame. Most of these fans also come wired with a plug for easy installation in the garden. A typical 110v fan works at about 50CFM, with a noise level of 40dBA. These units have 40% more airflow than PC fans, which makes them a good choice for cooling small spaces (and also for DIY carbon filters such as this one).
12v PC fans This is a basic and cheap solution for ventilation and cooling in Space Buckets. PC fans are easy to find and recycle, and they provide enough airflow to extract the heat from your garden. Keep in mind that in order to run PC fans you need a 12v power supply, which are also cheap and readily available. With 1A you can run 2 fans safely, though your mileage may vary and testing is always recommended. A typical 12v PC fan works at about 30 CFM (Cubic Feet per Minute) with a noise level of 26 dBA. These are usually not strong enough to handle carbon filters.
Booster fans Duct fans are a great (and often overlooked) alternative for cooling Space Buckets, as they provide good airflow: the 4' version provides about 100 CFM, which is 70% more than standard PC fans. These Booster fans can be used in high temperature situations to extract the heat from the bulbs. These fans also work at line voltage (110v or 220v), and they come already wired with a plug, so installation is a matter of fitting it in the bucket and turning it on. They're a cheaper kind of inline fan, which can be used for odor carbon filtering.
USB fans Most cheap USB fans are built with brushed rather than brushless motors and are not likely to last more than a few months (see this comparison thread). However there are some higher end USB fans (for example the Stylepie Fun Fun Fan) that are brushless and will last a long time. A sewn carbon filter can be put on this fan but its ability to push enough air through is debatable.