What's the best size? For most workshops and households, a 10- to 14-gallon wet-dry vac is the optimal size. These models can handle most jobs, are convenient to store and move around, and still offer adequate suction. However, for big cleanups such as collecting wood chips, a 16- to 20-gallon tank is more convenient. On the other hand, smaller wet-dry vacuums with tanks that hold 5 or 6 gallons are handier for cleaning a house or car because they're easier to transport. Portable 1- to 3-gallon vacuums are the easiest of all to haul around, but they provide a lot less suction and capacity.
What hose size do you need? For general workshop jobs, such as vacuuming wood dust and shavings, experts recommend a 2.25- to 2.5-inch diameter hose. Narrower hoses tend to clog. However, if you're using power tools in a workshop, you'll need a smaller, flexible hose that fits the dust ports on your tools. Some shop vacuums for workshop use come with both a wider hose and a cuff adapter that can secure it to a tool's dust port.
How much will accessories cost? Many of the tool attachments, filters and dust bags designed for consumer-grade wet-dry vacuums can be used on more than one brand, but higher-end wet-dry vacs often require more expensive supplies. You may also want to budget for extra accessories -- not just dust bags or filters, but a longer, bigger or more flexible hose, or more extension wands for reaching high ceilings.
Do you plan to vacuum liquids frequently? If you plan to vacuum water and other liquid messes frequently, look for a model with a drain spout. This feature lets you hook up a pump and garden hose to drain the tank without having to lift and move the whole device. Some wet-dry vacs come with a pump, while others can be hooked up to an aftermarket pump.
Is air quality a concern? If you're trying to minimize dust pollution in your home or work area, seek out a shop vacuum that includes a HEPA filter and can accept dust collection bags. These features remove the smallest particles from the air.
Where will you store your wet-dry vac? Shop vacuums of equal capacity vary in height and shape. If you have ample storage space, size may be of little concern. However, if you plan to store your wet-dry vacuum under a shelf in a workshop or in a tight space, measure your available space to ensure you choose a model that will fit. If your home or garage is limited on storage, consider a wall-mounted wet-dry vacuum.
Wet-dry vacuums come with warranties ranging from a single year to lifetime. A good warranty comes in handy if you're one of the unlucky few owners whose wet-dry vac breaks down or burns out, but for most users, a bigger concern is the cost of replacing filters and dust collection bags. Filters, depending on type, cost anywhere from $10 to over $100; however, some filters are washable, so they need to be replaced less often. Canister bags, or dust collection bags, typically cost between $3 and $8 apiece.
Attachments can be another added cost. Most wet-dry vacuums come with at least a few attachments for different cleaning tasks, including extension wands for greater reach. However, if your wet-dry vac doesn't come with the attachments you need, purchasing them separately will add to the total cost. If you also own an upright or canister vacuum with attachments, you can probably use them with a wet-dry vacuum that has a 1.25-inch hose.