Price matters, but it's less important than getting a machine that does the things you need it to do. As a remodeler, I want a vacuum that can hold a large amount of debris, automatically collect dust from power tools, and be used for cleanup at all stages of a project. If you don't do much demolition and don't collect dust from power tools, you may be better served by a smaller, more basic unit.
Backpack or canister. Small and light, backpack-style vacuums are designed for mobility. They're handy when you're working on uneven terrain (such as outdoors and on stairs) or in cluttered areas where you don't want to handle a long hose. Just remember that operators must bear the weight of the machine and its contents.
Since canister vacuums typically have wheels, you can move them around even when they're filled with heavy debris. Large wheels are better than small ones because they make it easier to roll the machine over cords and rough ground. And it's good if the wheels have locks, because then you can place the vacuum on a slope or stair landing without having to worry that it will go somewhere it shouldn't.
Tool activation. A power tool that is used to grind or sand material containing lead must be equipped with a dust port and connected to a HEPA vacuum so that dust is captured as it is generated. Many vacuums have built-in electrical receptacles that you can plug tools into. When the tool comes on, the vacuum is automatically activated, which means you don't have to run the vacuum continuously or constantly turn it on and off. Most of these vacuums run for several seconds after the tool turns off to clear the hose of dust.
HEPA filters are designed to stop 99.97 percent of particles down to 0.3 microns in size. The oversize filter in this Mastercraft model (far left) installs over a prefilter, which extends its life by capturing most of the fine dust that gets through the collection bag. Like most HEPA filters, the Dustless Technologies filter (above left) is gasketed to prevent air from leaking through. The rectangular filter in Festool's vacuum (left) fits into a frame
If the vacuum does not have a tool-activated switch, it can still be activated by a tool. The least expensive way to do this is to plug the tool and vac into an auxiliary device that sends power to the vacuum when the tool comes on. Two examples are the iVac Switch Box (MBright Tools, 613-826-2200, ivacswitch.com) and the i-Socket Autoswitch (dgcproducts.com). You could also use a Tool-Pod Wireless Remote System (800-568-3949, dustlesstechnologies.com), a $210 accessory that allows a tool plugged into one circuit to activate a vacuum plugged into another.
Variable suction. For most kinds of cleanup you'll want the maximum amount of suction. But for tasks like collecting dust from sanders (which won't move freely if there is too much suction) and vacuuming flexible surfaces (such as plastic dust barriers and fabrics), it's best to turn the suction down. Tool-activated models typically have variable suction control; if the vacuum does not have this feature, and there is a secondary opening (a covered hole) on the wand, you can reduce suction by uncovering the opening.
Keeping it clean. Since the vacuum and accessories will be exposed to lead dust, it's important that they be easy to clean so you won't contaminate your vehicle or the rooms you carry them through. Look for smooth surfaces free of dust-trapping indentations, and consider buying an antistatic hose, which will attract and retain less dust.
Some models include (or can be equipped with) a cap to plug the hole in the front of the machine so that dust can't come out if the hose is removed for transport. The cap should be connected to the vac so it doesn't get lost between uses. Another method is to temporarily cover the hole with duct tape.