Shop vacs come in small (2-6 gallons), medium (6-14 gallons), and high capacity (14-18 gallons). The medium capacity will suit most needs — it’s sufficient for most indoor and outdoor cleaning tasks homeowners face.
Air power, or air-watts, refers to the suction power of your shop vac. A higher air power is important if you plan to vacuum heavier objects like nuts and bolts.
In addition to size, you’ll be faced with another choice: plastic or stainless steel tank. Plastic tanks are lighter and less prone to dents, but stainless steel tanks are easier to clean and more durable in the long run.
Expand cleaning capabilities by shopping for a wet/dry vac with attachments. The type and number of attachments may vary, but some of the most frequently used are a utility nozzle, wet nozzle, and crevice tool. Extension wand attachments might also be important to you if you want to extend the reach of your shop vac into tight spaces or overhead areas to clear cobwebs, dust, and more.
You should also consider whether or not a shop vac has onboard attachment storage. Some models feature a toolbox-like top that stores attachments. Other models have snap-on storage for wands, nozzles, and more. Many models, however, lack attachment storage. Consider whether you want or need attachments within reach at all times when using your shop vac.